fix r & d not working from Metro sometimes

Summary:
Changelog:
[iOS][Fixed] - fix `r` & `d` not working from Metro sometimes

While investigating these bugs, I've come across some cases where `r` (Reload) & `d` (Open Dev Menu) not working in Metro.

* T206141946 / [WP: Reconnecting dev tools does not work after restarting the app](https://fb.workplace.com/groups/rn.debugger.feedback/posts/1107620434125533)
* T206754760 / [WP: Can't launch DevTools from Metro sometimes](https://fb.workplace.com/groups/rn.debugger.feedback/posts/1112235073664069/)

This is because when we
1. Start app without Metro
1. Start Metro
1. Reload from Dev Menu (rage shake)

`RCTPackagerConnection` did not get notified about the change in bundle URL. It'd stay "listening" to the commands from the local bundle instead of Metro
.

Differential Revision: D65973309

packages/react-native/React/DevSupport/RCTPackagerConnection.mm

@@ -20,6 +20,7 @@
 #import <React/RCTLog.h>
 #import <React/RCTPackagerClient.h>
 #import <React/RCTReconnectingWebSocket.h>
+#import <React/RCTReloadCommand.h>
 #import <React/RCTUtils.h>
 
 #if RCT_DEV
@@ -44,6 +45,7 @@ @implementation RCTPackagerConnection {
   NSString *_serverHostPortForSocket;
   NSString *_serverSchemeForSocket;
   id _bundleURLChangeObserver;
+  id _reloadWithPotentiallyNewURLObserver;
   uint32_t _nextToken;
   std::vector<Registration<RCTNotificationHandler>> _notificationRegistrations;
   std::vector<Registration<RCTRequestHandler>> _requestRegistrations;
@@ -78,6 +80,13 @@ - (instancetype)init
                                                       usingBlock:^(NSNotification *_Nonnull __unused note) {
                                                         [weakSelf bundleURLSettingsChanged];
                                                       }];
+    _reloadWithPotentiallyNewURLObserver =
+        [[NSNotificationCenter defaultCenter] addObserverForName:RCTTriggerReloadCommandNotification
+                                                          object:nil
+                                                           queue:[NSOperationQueue mainQueue]
+                                                      usingBlock:^(NSNotification *_Nonnull __unused note) {
+                                                        [weakSelf bundleURLSettingsChanged];
+                                                      }];
   }
   return self;
 }
@@ -119,6 +128,8 @@ - (void)stop
   }
   [[NSNotificationCenter defaultCenter] removeObserver:_bundleURLChangeObserver];
   _bundleURLChangeObserver = nil;
+  [[NSNotificationCenter defaultCenter] removeObserver:_reloadWithPotentiallyNewURLObserver];
+  _reloadWithPotentiallyNewURLObserver = nil;
   _socketConnected = NO;
   [_socket stop];
   _socket = nil;