BREAKING: Android: Correct value of Dimensions.get('screen').fontScale

Summary:
The PR description has been updated to reflect the new approach.

**Breaking Change Summary**

On Android, the following properties now return a different number:
  - `Dimensions.get('window').fontScale`
  - `Dimensions.get('screen').fontScale`
  - `PixelRatio.getFontScale()`

This is a breaking change to anyone who was using these properties because the meaning of these properties has now changed.

These properties used to return a value representing font scale times density ([`DisplayMetrics.scaledDensity`](https://developer.android.com/reference/android/util/DisplayMetrics.html#scaledDensity)). Now they return a value representing just font scale ([`Configuration.fontScale`](https://developer.android.com/reference/android/content/res/Configuration.html#fontScale)).

**PR Description**

This PR changes a few things:
  - Correctly exposes the font scale to JavaScript as `Dimensions.get('screen').fontScale`. UIManager was exporting `DisplayMetrics.scaledDensity` under the name `fontScale`. How
Closes https://github.com/facebook/react-native/pull/11008

Differential Revision: D4558207

Pulled By: astreet

fbshipit-source-id: 096ce7b28051325dfd45fdb2a14b5e9b7d3bc46f

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModuleConstants.java

@@ -16,6 +16,8 @@ import android.util.DisplayMetrics;
 import android.view.accessibility.AccessibilityEvent;
 import android.widget.ImageView;
 
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.common.MapBuilder;
 import com.facebook.react.uimanager.events.TouchEventType;
 
@@ -81,7 +83,7 @@ import com.facebook.react.uimanager.events.TouchEventType;
         .build();
   }
 
-  public static Map<String, Object> getConstants() {
+  public static Map<String, Object> getConstants(float fontScale) {
     HashMap<String, Object> constants = new HashMap<String, Object>();
     constants.put(
         "UIView",
@@ -95,35 +97,9 @@ import com.facebook.react.uimanager.events.TouchEventType;
                 "ScaleAspectCenter",
                 ImageView.ScaleType.CENTER_INSIDE.ordinal())));
 
-    DisplayMetrics displayMetrics = DisplayMetricsHolder.getWindowDisplayMetrics();
-    DisplayMetrics screenDisplayMetrics = DisplayMetricsHolder.getScreenDisplayMetrics();
     constants.put(
         "Dimensions",
-        MapBuilder.of(
-            "windowPhysicalPixels",
-            MapBuilder.of(
-                "width",
-                displayMetrics.widthPixels,
-                "height",
-                displayMetrics.heightPixels,
-                "scale",
-                displayMetrics.density,
-                "fontScale",
-                displayMetrics.scaledDensity,
-                "densityDpi",
-                displayMetrics.densityDpi),
-        "screenPhysicalPixels",
-        MapBuilder.of(
-            "width",
-            screenDisplayMetrics.widthPixels,
-            "height",
-            screenDisplayMetrics.heightPixels,
-            "scale",
-            screenDisplayMetrics.density,
-            "fontScale",
-            screenDisplayMetrics.scaledDensity,
-            "densityDpi",
-            screenDisplayMetrics.densityDpi)));
+        getDimensionsConstants(fontScale));
 
     constants.put(
         "StyleConstants",
@@ -157,4 +133,29 @@ import com.facebook.react.uimanager.events.TouchEventType;
 
     return constants;
   }
+
+  public static WritableMap getDimensionsConstants(float fontScale) {
+    DisplayMetrics windowDisplayMetrics = DisplayMetricsHolder.getWindowDisplayMetrics();
+    DisplayMetrics screenDisplayMetrics = DisplayMetricsHolder.getScreenDisplayMetrics();
+
+    WritableMap windowDisplayMetricsMap = Arguments.createMap();
+    windowDisplayMetricsMap.putInt("width", windowDisplayMetrics.widthPixels);
+    windowDisplayMetricsMap.putInt("height", windowDisplayMetrics.heightPixels);
+    windowDisplayMetricsMap.putDouble("scale", windowDisplayMetrics.density);
+    windowDisplayMetricsMap.putDouble("fontScale", fontScale);
+    windowDisplayMetricsMap.putDouble("densityDpi", windowDisplayMetrics.densityDpi);
+
+    WritableMap screenDisplayMetricsMap = Arguments.createMap();
+    screenDisplayMetricsMap.putInt("width", screenDisplayMetrics.widthPixels);
+    screenDisplayMetricsMap.putInt("height", screenDisplayMetrics.heightPixels);
+    screenDisplayMetricsMap.putDouble("scale", screenDisplayMetrics.density);
+    screenDisplayMetricsMap.putDouble("fontScale", fontScale);
+    screenDisplayMetricsMap.putDouble("densityDpi", screenDisplayMetrics.densityDpi);
+
+    WritableMap dimensionsMap = Arguments.createMap();
+    dimensionsMap.putMap("windowPhysicalPixels", windowDisplayMetricsMap);
+    dimensionsMap.putMap("screenPhysicalPixels", screenDisplayMetricsMap);
+    
+    return dimensionsMap;
+  }
 }