destroy callbacks even if they aren't called, when java object is destroyed

Summary:
JSI callbacks are only destroyed if the callback is called. If the callback is never called, we're potentially leaking a lot of callbacks.

To mitigate this, we add a wrapper object that is owned by the std::function. Whenever the std::function is destroyed, the wrapper is destroyed and it deallocates the callback as well.

Changelog: [Internal]

Reviewed By: RSNara

Differential Revision: D27436402

fbshipit-source-id: d153640d5d7988c7fadaf2cb332ec00dadd0689a

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

@@ -23,6 +23,13 @@ public class ReactFeatureFlags {
    */
   public static volatile boolean useTurboModules = false;
 
+  /**
+   * Should application use the new TM callback manager in Cxx? This is assumed to be a sane
+   * default, but it's new. We will delete once (1) we know it's safe to ship and (2) we have
+   * quantified impact.
+   */
+  public static volatile boolean useTurboModulesRAIICallbackManager = false;
+
   /** Should we dispatch TurboModule methods with promise returns to the NativeModules thread? */
   public static volatile boolean enableTurboModulePromiseAsyncDispatch = false;