Use static constants instead of strings when referring to View Managers and Native Modules

Summary: Using strings to refer to Native Modules and View Managers in ReactPackages are prone to error. The compiler replaces the constants with the actual strings anyway, so using constants gives us  better type safety

Reviewed By: achen1

Differential Revision: D12843649

fbshipit-source-id: 7a7c6c854c8689193f40df92dc8426a3b37f82c8

Author: axe-fb

ReactViewPagerManager.java

@@ -28,7 +28,7 @@
 @ReactModule(name = ReactViewPagerManager.REACT_CLASS)
 public class ReactViewPagerManager extends ViewGroupManager<ReactViewPager> {
 
-  protected static final String REACT_CLASS = "AndroidViewPager";
+  public static final String REACT_CLASS = "AndroidViewPager";
 
   public static final int COMMAND_SET_PAGE = 1;
   public static final int COMMAND_SET_PAGE_WITHOUT_ANIMATION = 2;