Create MC to verify impact of eager initialization of fabric classes

Summary:
This diff creates a MC to verify impact of eager initialization of fabric classes, the purpose is to remove this code, but before doing that I would like to verify what's the impact.

changelog: [internal] internal

Reviewed By: sammy-SC

Differential Revision: D28223943

fbshipit-source-id: 6f7c4701fb730fe1c0629ec13ead592ff619373f

ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -61,6 +61,9 @@ public class ReactFeatureFlags {
   /** Feature flag to configure eager initialization of Fabric */
   public static boolean eagerInitializeFabric = false;
 
+  /** Feature flag to configure eager initialization classes of Fabric */
+  public static boolean eagerInitializeFabricClasses = false;
+
   /** Enables Static ViewConfig in RN Android native code. */
   public static boolean enableExperimentalStaticViewConfigs = false;
 

ReactAndroid/src/main/java/com/facebook/react/fabric/FabricJSIModuleProvider.java

@@ -15,6 +15,7 @@
 import com.facebook.react.bridge.ReactApplicationContext;
 import com.facebook.react.bridge.UIManager;
 import com.facebook.react.bridge.queue.MessageQueueThread;
+import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.fabric.events.EventBeatManager;
 import com.facebook.react.fabric.events.EventEmitterWrapper;
 import com.facebook.react.fabric.events.FabricEventEmitter;
@@ -63,7 +64,9 @@ public UIManager get() {
         Systrace.TRACE_TAG_REACT_JAVA_BRIDGE, "FabricJSIModuleProvider.registerBinding");
     final Binding binding = new Binding();
     // TODO T31905686: remove this call
-    loadClasses();
+    if (ReactFeatureFlags.eagerInitializeFabricClasses) {
+      loadClasses();
+    }
     MessageQueueThread jsMessageQueueThread =
         mReactApplicationContext
             .getCatalystInstance()