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/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);