[fabric] Add View focus/blur event emitting on first responder change

Summary: This diff overrides the first responder tracking methods to submit focus/blur events when the native view becomes the first responder (focus) and resigns the first responder state (blur).

Test Plan:
* Update a view to log to the console when it is focused/blurred
* Run Zeratul with Fabric enabled
* Focus/blur the view and check the logs to verify that the event handlers are being called

 https://pxl.cl/4n99N

Reviewers: shawndempsey, #rn-desktop

Reviewed By: shawndempsey

Differential Revision: https://phabricator.intern.facebook.com/D53931157

Author: Nick Lefever

packages/react-native/React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -1510,6 +1510,38 @@ - (BOOL)didActivateAccessibilityCustomAction:(UIAccessibilityCustomAction *)acti
   }
 }
 
+#if TARGET_OS_OSX // [macOS
+
+#pragma mark - Focus Events
+
+- (BOOL)becomeFirstResponder
+{
+  if (![super becomeFirstResponder]) {
+    return NO;
+  }
+
+  if (_eventEmitter) {
+    _eventEmitter->onFocus();
+  }
+
+  return YES;
+}
+
+-  (BOOL)resignFirstResponder
+{
+  if (![super resignFirstResponder]) {
+    return NO;
+  }
+
+  if (_eventEmitter) {
+    _eventEmitter->onBlur();
+  }
+
+  return YES;
+}
+
+#endif // macOS]
+
 - (SharedTouchEventEmitter)touchEventEmitterAtPoint:(CGPoint)point
 {
   return _eventEmitter;