introduce logic for shared native module queue

Summary:
Changelog: [Internal]

currently, each native module creates a new module queue if `methodQueue` is not overridden in the native module.

we want to see if we can use a single execution queue for a few reasons:
- parity with android's queue model
- performance: creating so many queues... for what? the overhead of this feels like it exceeds any potential benefit
- set us up to remove the assocs from the module to the method queue, which will allow us to deprecate `synthesize methodQueue` and `-(dispatch_queue_t)moduleQueue` API.

in this QE, we just start with replacing the KVO assoc'd queue with the shared module queue.

Differential Revision: D50398635

packages/react-native/ReactCommon/react/nativemodule/core/platform/ios/ReactCommon/RCTTurboModuleManager.mm

@@ -206,6 +206,9 @@ @implementation RCTTurboModuleManager {
 
   RCTBridgeProxy *_bridgeProxy;
   RCTBridgeModuleDecorator *_bridgeModuleDecorator;
+
+  BOOL _enableSharedModuleQueue;
+  dispatch_queue_t _sharedModuleQueue;
 }
 
 - (instancetype)initWithBridge:(RCTBridge *)bridge
@@ -221,6 +224,7 @@ - (instancetype)initWithBridge:(RCTBridge *)bridge
     _bridgeProxy = bridgeProxy;
     _bridgeModuleDecorator = bridgeModuleDecorator;
     _invalidating = false;
+    _enableSharedModuleQueue = NO;
 
     if (RCTTurboModuleInteropEnabled()) {
       NSMutableDictionary<NSString *, id<RCTBridgeModule>> *legacyInitializedModules = [NSMutableDictionary new];
@@ -685,8 +689,12 @@ - (BOOL)_shouldCreateObjCModule:(Class)moduleClass
    * following if condition's block.
    */
   if (!methodQueue) {
-    NSString *methodQueueName = [NSString stringWithFormat:@"com.facebook.react.%sQueue", moduleName];
-    methodQueue = dispatch_queue_create(methodQueueName.UTF8String, DISPATCH_QUEUE_SERIAL);
+    if (_enableSharedModuleQueue) {
+      methodQueue = [self _sharedModuleQueue];
+    } else {
+      NSString *methodQueueName = [NSString stringWithFormat:@"com.facebook.react.%sQueue", moduleName];
+      methodQueue = dispatch_queue_create(methodQueueName.UTF8String, DISPATCH_QUEUE_SERIAL);
+    }
 
     if (moduleHasMethodQueueGetter) {
       /**
@@ -1067,4 +1075,12 @@ - (void)_invalidateModules
   _legacyModuleCache.clear();
 }
 
+- (dispatch_queue_t)_sharedModuleQueue
+{
+  if (!_sharedModuleQueue) {
+    _sharedModuleQueue = dispatch_queue_create("com.meta.react.turbomodulemanager.queue", DISPATCH_QUEUE_SERIAL);
+  }
+  return _sharedModuleQueue;
+}
+
 @end