Convert ReactMarkerConsts back to enum, use @CountEnum

Summary: Reverting D9304307 and also adding CountEnum annotation to ReactMarkerConstants. This way we get the typesafety of the enum with the optimization of converting to int in production builds. More on the count: https://our.intern.facebook.com/intern/wiki/Android-java-transforms/the-count/

Reviewed By: achen1

Differential Revision: D9623235

fbshipit-source-id: ab992e7edb6cf999f5f122faee31075a63782411