Align View creation flow between Fabric and non-Fabric

Summary:
Ship responsibility for most View creation logic to ViewManager, where it already largely lies, and simplify code in Fabric and non-Fabric mounting layers.

Notably, some of this work was *already* being duplicated so we can expect an extremely tiny perf gain here.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D26742711

fbshipit-source-id: 4213766d4cd366bc69cd47d4654f7b269bb9e7f4

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

@@ -122,7 +122,10 @@ public abstract class ViewManager<T extends View, C extends ReactShadowNode>
   /**
    * Subclasses should return a new View instance of the proper type. This is an optional method
    * that will call createViewInstance for you. Override it if you need props upon creation of the
-   * view.
+   * view, or state.
+   *
+   * <p>If you override this method, you *must* guarantee that you you're handling updateProperties,
+   * view.setId, addEventEmitters, and updateState/updateExtraData properly!
    *
    * @param reactTag reactTag that should be set as ID of the view instance
    * @param reactContext ReactContext used to initialize view instance
@@ -140,6 +143,7 @@ public abstract class ViewManager<T extends View, C extends ReactShadowNode>
     if (initialProps != null) {
       updateProperties(view, initialProps);
     }
+    // Only present in Fabric; but always present in Fabric.
     if (stateWrapper != null) {
       Object extraData = updateState(view, initialProps, stateWrapper);
       if (extraData != null) {