Fix cannot working Modal's onDismiss. (#29882)

Summary:
Fixes: https://github.com/facebook/react-native/issues/29455

Modal's onDismiss is not called on iOS.
This issue occurred the commit https://github.com/facebook/react-native/commit/bd2b7d6c0366b5f19de56b71cb706a0af4b0be43 and was fixed the commit https://github.com/facebook/react-native/commit/27a3248a3b37410b5ee6dda421ae00fa485b525c.
However, the master and stable-0.63 branches do not have this modified commit applied to them.

## Changelog

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[iOS] [Fixed] - Modal's onDismiss prop will now be called successfully.

Pull Request resolved: https://github.com/facebook/react-native/pull/29882

Test Plan:
Tested on iOS with this change:

1. Set function Modal's onDismiss prop.
1. Set Modal's visible props is true. (show Modal)
1. Set Modal's visible props is false. (close Modal)
1. The set function in onDismiss is called.

Reviewed By: shergin

Differential Revision: D24648412

Pulled By: hramos

fbshipit-source-id: acf28fef21420117c845d3aed97e47b5dd4e9390

ReactAndroid/src/main/java/com/facebook/react/viewmanagers/jni/react/renderer/components/rncore/EventEmitters.cpp

@@ -129,6 +129,13 @@ void ModalHostViewEventEmitter::onShow(OnShow event) const {
     return payload;
   });
 }
+void ModalHostViewEventEmitter::onDismiss(OnDismiss event) const {
+  dispatchEvent("dismiss", [event=std::move(event)](jsi::Runtime &runtime) {
+    auto payload = jsi::Object(runtime);
+    
+    return payload;
+  });
+}
 void ModalHostViewEventEmitter::onOrientationChange(OnOrientationChange event) const {
   dispatchEvent("orientationChange", [event=std::move(event)](jsi::Runtime &runtime) {
     auto payload = jsi::Object(runtime);

ReactAndroid/src/main/java/com/facebook/react/viewmanagers/jni/react/renderer/components/rncore/EventEmitters.h

@@ -196,6 +196,10 @@ class ModalHostViewEventEmitter : public ViewEventEmitter {
       
     };
 
+  struct OnDismiss {
+      
+    };
+
   enum class OnOrientationChangeOrientation {
     Portrait,
     Landscape
@@ -216,6 +220,8 @@ class ModalHostViewEventEmitter : public ViewEventEmitter {
 
   void onShow(OnShow value) const;
 
+  void onDismiss(OnDismiss value) const;
+
   void onOrientationChange(OnOrientationChange value) const;
 };