Apply custom headers in RCTReconnectingWebSocket (#55611)

Summary:
Pull Request resolved: #55611

Inject custom devsupport headers into the HMR WebSocket connection. Changes from `initWithURL:` to `initWithURLRequest:` so headers can be set on the HTTP upgrade handshake.

Changelog:
[Internal] [Changed] -

Reviewed By: cipolleschi

Differential Revision: D93596718

fbshipit-source-id: ab028d0e03e11f0efde000d19943693439236dbc

Author: cortinico

packages/react-native/Libraries/WebSocket/RCTReconnectingWebSocket.m

@@ -9,6 +9,7 @@
 
 #import <React/RCTConvert.h>
 #import <React/RCTDefines.h>
+#import <React/RCTDevSupportHttpHeaders.h>
 
 #import <SocketRocket/SRWebSocket.h>
 
@@ -46,7 +47,9 @@ - (void)start
 {
   [self stop];
   _stopped = NO;
-  _socket = [[SRWebSocket alloc] initWithURL:_url];
+  NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:_url];
+  [[RCTDevSupportHttpHeaders sharedInstance] applyHeadersToRequest:request];
+  _socket = [[SRWebSocket alloc] initWithURLRequest:request];
   _socket.delegate = self;
   [_socket setDelegateDispatchQueue:_delegateDispatchQueue];
   [_socket open];