Start core marker earlier

Summary: Moving up when we start the CORE marker to `FbReactFragment.onFragmentCreate` on FB4A. Right now the CORE marker gets started with CREATE_REACT_CONTEXT_START, since it's possible for the instance manager to be created before TTI begins. We address this in HOME_TTI by collecting the getInstanceManager time, comparing to TTI start, and using that as bridgeStartupStartTime. Ideally, though, we'd just start the CORE marker at the right time so we can use it independently to measure RN startup. This diff moves up CORE start time to `onFragmentCreate` (even before `getReactInstanceManager`)

Reviewed By: alexeylang

Differential Revision: D10094921

fbshipit-source-id: 77986535915f8e81d4d2c5b9108cbed40d1a75be

ReactAndroid/src/main/java/com/facebook/react/bridge/ReactMarkerConstants.java

@@ -88,4 +88,5 @@ public enum ReactMarkerConstants {
   REGISTER_JS_SEGMENT_START,
   REGISTER_JS_SEGMENT_STOP,
   VM_INIT,
+  ON_FRAGMENT_CREATE,
 }