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/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;