Add Appearance module

Summary:
Android implementation of the Appearance native module. Exposes the user's preferred color scheme: "dark" for Night theme ON, "light" for Night theme OFF.

Emits a `appearanceChanged` event when the current uiMode configuration changes.

To make your app handle Night mode changes, make sure to do the following:

* Declare your Activity can handle uiMode configuration changes (https://developer.android.com/preview/features/darktheme#java):
```
android:configChanges="uiMode"
```
* Make sure to pass the configuration changed activity lifecycle callback from your ReactActivity:
```
Override
protected void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged();

    if (mReactInstanceManager != null) {
        mReactInstanceManager.onConfigurationChanged(newConfig);
    }
}
```

### RNTester

Adds the AppearanceExample to RNTester on Android.

Changelog:

[Android][Added] - New Appearance module exposes the user's current Night theme preference

Reviewed By: makovkastar

Differential Revision: D16942161

fbshipit-source-id: d24a8ff800a1c5f70f4efdec6891396c2078067e

ReactAndroid/src/main/java/com/facebook/react/BUCK

@@ -33,6 +33,7 @@ rn_android_library(
         react_native_target("java/com/facebook/react/module/annotations:annotations"),
         react_native_target("java/com/facebook/react/module/model:model"),
         react_native_target("java/com/facebook/react/modules/appregistry:appregistry"),
+        react_native_target("java/com/facebook/react/modules/appearance:appearance"),
         react_native_target("java/com/facebook/react/modules/core:core"),
         react_native_target("java/com/facebook/react/modules/debug:debug"),
         react_native_target("java/com/facebook/react/modules/fabric:fabric"),

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -34,6 +34,7 @@ import static com.facebook.systrace.Systrace.TRACE_TAG_REACT_JS_VM_CALLS;
 import android.app.Activity;
 import android.content.Context;
 import android.content.Intent;
+import android.content.res.Configuration;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.Process;
@@ -78,6 +79,7 @@ import com.facebook.react.devsupport.RedBoxHandler;
 import com.facebook.react.devsupport.interfaces.DevBundleDownloadListener;
 import com.facebook.react.devsupport.interfaces.DevSupportManager;
 import com.facebook.react.devsupport.interfaces.PackagerStatusCallback;
+import com.facebook.react.modules.appearance.AppearanceModule;
 import com.facebook.react.modules.appregistry.AppRegistry;
 import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;
 import com.facebook.react.modules.core.DeviceEventManagerModule;
@@ -712,6 +714,17 @@ public class ReactInstanceManager {
     }
   }
 
+  /** Call this from {@link Activity#onConfigurationChanged()}. */
+  @ThreadConfined(UI)
+  public void onConfigurationChanged(Configuration newConfig) {
+    UiThreadUtil.assertOnUiThread();
+
+    ReactContext currentContext = getCurrentReactContext();
+    if (currentContext != null) {
+      currentContext.getNativeModule(AppearanceModule.class).onConfigurationChanged();
+    }
+  }
+
   @ThreadConfined(UI)
   public void showDevOptionsDialog() {
     UiThreadUtil.assertOnUiThread();

ReactAndroid/src/main/java/com/facebook/react/modules/appearance/AppearanceModule.java

@@ -0,0 +1,92 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * <p>This source code is licensed under the MIT license found in the LICENSE file in the root
+ * directory of this source tree.
+ */
+package com.facebook.react.modules.appearance;
+
+import android.content.Context;
+import android.content.res.Configuration;
+import android.os.Build;
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.module.annotations.ReactModule;
+import com.facebook.react.modules.core.DeviceEventManagerModule.RCTDeviceEventEmitter;
+
+/** Module that exposes the user's preferred color scheme. For API >= 29. */
+@ReactModule(name = AppearanceModule.NAME)
+public class AppearanceModule extends ReactContextBaseJavaModule {
+  public static final String NAME = "Appearance";
+
+  private static final String APPEARANCE_CHANGED_EVENT_NAME = "appearanceChanged";
+  private static final int ANDROID_TEN = 29;
+
+  private String mColorScheme = "light";
+
+  public AppearanceModule(ReactApplicationContext reactContext) {
+    super(reactContext);
+
+    mColorScheme = colorSchemeForCurrentConfiguration(reactContext);
+  }
+
+  private static String colorSchemeForCurrentConfiguration(Context context) {
+    // TODO: (hramos) T52929922: Switch to Build.VERSION_CODES.ANDROID_TEN or equivalent
+    if (Build.VERSION.SDK_INT >= ANDROID_TEN) {
+      int currentNightMode =
+          context.getResources().getConfiguration().uiMode & Configuration.UI_MODE_NIGHT_MASK;
+      switch (currentNightMode) {
+        case Configuration.UI_MODE_NIGHT_NO:
+          return "light";
+        case Configuration.UI_MODE_NIGHT_YES:
+          return "dark";
+      }
+    }
+
+    return "light";
+  }
+
+  @Override
+  public String getName() {
+    return NAME;
+  }
+
+  @ReactMethod(isBlockingSynchronousMethod = true)
+  public String getColorScheme() {
+    mColorScheme = colorSchemeForCurrentConfiguration(getReactApplicationContext());
+    return mColorScheme;
+  }
+
+  /** Stub */
+  @ReactMethod
+  public void addListener(String eventName) {}
+
+  /** Stub */
+  @ReactMethod
+  public void removeListeners(double count) {}
+
+  /*
+   * Call this from your root activity whenever configuration changes. If the
+   * color scheme has changed, an event will emitted.
+   */
+  public void onConfigurationChanged() {
+    String newColorScheme = colorSchemeForCurrentConfiguration(getReactApplicationContext());
+    if (!mColorScheme.equals(newColorScheme)) {
+      mColorScheme = newColorScheme;
+      emitAppearanceChanged(mColorScheme);
+    }
+  }
+
+  /** Sends an event to the JS instance that the preferred color scheme has changed. */
+  public void emitAppearanceChanged(String colorScheme) {
+    WritableMap appearancePreferences = Arguments.createMap();
+    appearancePreferences.putString("colorScheme", colorScheme);
+
+    getReactApplicationContext()
+        .getJSModule(RCTDeviceEventEmitter.class)
+        .emit(APPEARANCE_CHANGED_EVENT_NAME, appearancePreferences);
+  }
+}

ReactAndroid/src/main/java/com/facebook/react/modules/appearance/BUCK

@@ -0,0 +1,19 @@
+load("//tools/build_defs/oss:rn_defs.bzl", "react_native_dep", "react_native_target", "rn_android_library")
+
+rn_android_library(
+    name = "appearance",
+    srcs = glob(["**/*.java"]),
+    is_androidx = True,
+    visibility = [
+        "PUBLIC",
+    ],
+    deps = [
+        react_native_dep("third-party/java/jsr-305:jsr-305"),
+        react_native_dep("third-party/android/support-annotations:android-support-annotations"),
+        react_native_dep("third-party/android/androidx:annotation"),
+        react_native_target("java/com/facebook/react/bridge:bridge"),
+        react_native_target("java/com/facebook/react/common:common"),
+        react_native_target("java/com/facebook/react/module/annotations:annotations"),
+        react_native_target("java/com/facebook/react/modules/core:core"),
+    ],
+)

ReactAndroid/src/main/java/com/facebook/react/shell/BUCK

@@ -26,6 +26,7 @@ rn_android_library(
         react_native_target("java/com/facebook/react/devsupport:devsupport"),
         react_native_target("java/com/facebook/react/module/model:model"),
         react_native_target("java/com/facebook/react/modules/accessibilityinfo:accessibilityinfo"),
+        react_native_target("java/com/facebook/react/modules/appearance:appearance"),
         react_native_target("java/com/facebook/react/modules/appstate:appstate"),
         react_native_target("java/com/facebook/react/modules/blob:blob"),
         react_native_target("java/com/facebook/react/modules/camera:camera"),

ReactAndroid/src/main/java/com/facebook/react/shell/MainReactPackage.java

@@ -16,6 +16,7 @@ import com.facebook.react.module.annotations.ReactModuleList;
 import com.facebook.react.module.model.ReactModuleInfo;
 import com.facebook.react.module.model.ReactModuleInfoProvider;
 import com.facebook.react.modules.accessibilityinfo.AccessibilityInfoModule;
+import com.facebook.react.modules.appearance.AppearanceModule;
 import com.facebook.react.modules.appstate.AppStateModule;
 import com.facebook.react.modules.blob.BlobModule;
 import com.facebook.react.modules.blob.FileReaderModule;
@@ -71,6 +72,7 @@ import java.util.Map;
 @ReactModuleList(
     nativeModules = {
       AccessibilityInfoModule.class,
+      AppearanceModule.class,
       AppStateModule.class,
       BlobModule.class,
       FileReaderModule.class,
@@ -112,6 +114,8 @@ public class MainReactPackage extends TurboReactPackage {
     switch (name) {
       case AccessibilityInfoModule.NAME:
         return new AccessibilityInfoModule(context);
+      case AppearanceModule.NAME:
+        return new AppearanceModule(context);
       case AppStateModule.NAME:
         return new AppStateModule(context);
       case BlobModule.NAME:
@@ -210,6 +214,7 @@ public class MainReactPackage extends TurboReactPackage {
       Class<? extends NativeModule>[] moduleList =
           new Class[] {
             AccessibilityInfoModule.class,
+            AppearanceModule.class,
             AppStateModule.class,
             BlobModule.class,
             FileReaderModule.class,