Move UIManager annotations to separate package

Summary:
Moves ReactProp and ReactPropGroup to `com.facebook.react.uimanager.annotations`. This is needed
so that future annotation processor can run on code inside the com.facebook.react.uimanager package.

public

Reviewed By: astreet

Differential Revision: D2754842

fb-gh-sync-id: 3808c3e3f6c45e5897ecab88cd4175573c0c24e6

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

@@ -7,6 +7,7 @@ import android.os.Build;
 import android.view.View;
 
 import com.facebook.react.bridge.ReadableMap;
+import com.facebook.react.uimanager.annotations.ReactProp;
 
 /**
  * Base class that should be suitable for the majority of subclasses of {@link ViewManager}.