Fix border-stroke drawing after resetting border-radius (#28356)

Summary:
This PR fixes incorrect drawing of the View borders on Android, after changing the border-radius back to 0 *(and when no background-color is defined)*.

This happens because the `drawRoundedBackgroundWithBorders` function in ReactViewBackgroundDrawable changes the style on the Paint object to `STROKE`. This style is however never reverted back to `FILL`. This change ensures that the Paint style is set to `FILL` for the full execution of the `drawRectangularBackgroundWithBorders` function.

## Changelog

`[Android] [Fixed] - Fix border-drawing when changing border-radius back to 0`
Pull Request resolved: https://github.com/facebook/react-native/pull/28356

Test Plan:
**Faulty situation:**

![ezgif com-video-to-gif](https://user-images.githubusercontent.com/6184593/77153163-9759b280-6a99-11ea-82bb-33a1e0a4934c.gif)

**After the fix:**

![ezgif com-video-to-gif (1)](https://user-images.githubusercontent.com/6184593/77153825-c91f4900-6a9a-11ea-8e0c-a4280b9e72b8.gif)

Differential Revision: D21124741

Pulled By: shergin

fbshipit-source-id: 2044f8e8ad59a58df42b64d7ee8c4ad1d3b562f1

ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewBackgroundDrawable.java

@@ -998,10 +998,11 @@ public class ReactViewBackgroundDrawable extends Drawable {
   }
 
   private void drawRectangularBackgroundWithBorders(Canvas canvas) {
+    mPaint.setStyle(Paint.Style.FILL);
+    
     int useColor = ColorUtil.multiplyColorAlpha(mColor, mAlpha);
     if (Color.alpha(useColor) != 0) { // color is not transparent
       mPaint.setColor(useColor);
-      mPaint.setStyle(Paint.Style.FILL);
       canvas.drawRect(getBounds(), mPaint);
     }