Add support for shadowColor on Android (API >= 28) (#28650)

Summary:
This PR adds support for the `shadowColor` style on Android.

This is possible as of Android P using the `setOutlineAmbientShadowColor` and `setOutlineSpotShadowColor` View methods. The actual rendered color is a multiplication of the color-alpha, shadow-effect and elevation-value.

## Changelog

`[Android] [Added] - Add support for shadowColor on API level >= 28`
Pull Request resolved: https://github.com/facebook/react-native/pull/28650

Test Plan:
- Only execute code on Android P
- Added Android `BoxShadow` tests to RNTester app

![image](https://user-images.githubusercontent.com/6184593/79457137-fe627c80-7fef-11ea-8e88-3d9423a4f264.png)

Reviewed By: mdvacca

Differential Revision: D21125479

Pulled By: shergin

fbshipit-source-id: 14dcc023977d7a9d304fabcd3c90bcf34482f137

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

@@ -95,6 +95,15 @@ public abstract class BaseViewManager<T extends View, C extends LayoutShadowNode
     ViewCompat.setElevation(view, PixelUtil.toPixelFromDIP(elevation));
   }
 
+  @Override
+  @ReactProp(name = ViewProps.SHADOW_COLOR, defaultInt = Color.BLACK, customType = "Color")
+  public void setShadowColor(@NonNull T view, int shadowColor) {
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
+      view.setOutlineAmbientShadowColor(shadowColor);
+      view.setOutlineSpotShadowColor(shadowColor);
+    }
+  }
+
   @Override
   @ReactProp(name = ViewProps.Z_INDEX)
   public void setZIndex(@NonNull T view, float zIndex) {

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

@@ -54,6 +54,9 @@ public abstract class BaseViewManagerAdapter<T extends View>
   @Override
   public void setElevation(@NonNull T view, float elevation) {}
 
+  @Override
+  public void setShadowColor(@NonNull T view, int shadowColor) {}
+
   @Override
   public void setImportantForAccessibility(
       @NonNull T view, @Nullable String importantForAccessibility) {}

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

@@ -74,6 +74,10 @@ public abstract class BaseViewManagerDelegate<T extends View, U extends BaseView
       case ViewProps.ELEVATION:
         mViewManager.setElevation(view, value == null ? 0.0f : ((Double) value).floatValue());
         break;
+      case ViewProps.SHADOW_COLOR:
+        mViewManager.setShadowColor(
+            view, value == null ? 0 : ColorPropConverter.getColor(value, view.getContext()));
+        break;
       case ViewProps.IMPORTANT_FOR_ACCESSIBILITY:
         mViewManager.setImportantForAccessibility(view, (String) value);
         break;

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

@@ -43,6 +43,8 @@ public interface BaseViewManagerInterface<T extends View> {
 
   void setElevation(T view, float elevation);
 
+  void setShadowColor(T view, int shadowColor);
+
   void setImportantForAccessibility(T view, @Nullable String importantForAccessibility);
 
   void setNativeId(T view, @Nullable String nativeId);

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

@@ -140,6 +140,7 @@ public class ViewProps {
 
   public static final String TRANSFORM = "transform";
   public static final String ELEVATION = "elevation";
+  public static final String SHADOW_COLOR = "shadowColor";
   public static final String Z_INDEX = "zIndex";
   public static final String RENDER_TO_HARDWARE_TEXTURE = "renderToHardwareTextureAndroid";
   public static final String ACCESSIBILITY_LABEL = "accessibilityLabel";