introduce logic for shared native module queue (facebook#41042)

Summary:
Pull Request resolved: facebook#41042

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.

Reviewed By: cipolleschi

Differential Revision: D50398635

fbshipit-source-id: 0b194a5ae5269e843c7c537a973ee1d345ce1df4

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 +224,11 @@ - (instancetype)initWithBridge:(RCTBridge *)bridge
     _bridgeProxy = bridgeProxy;
     _bridgeModuleDecorator = bridgeModuleDecorator;
     _invalidating = false;
+    _enableSharedModuleQueue = NO;
+
+    if (_enableSharedModuleQueue) {
+      _sharedModuleQueue = dispatch_queue_create("com.meta.react.turbomodulemanager.queue", DISPATCH_QUEUE_SERIAL);
+    }
 
     if (RCTTurboModuleInteropEnabled()) {
       NSMutableDictionary<NSString *, id<RCTBridgeModule>> *legacyInitializedModules = [NSMutableDictionary new];
@@ -685,8 +693,12 @@ - (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 = _sharedModuleQueue;
+    } else {
+      NSString *methodQueueName = [NSString stringWithFormat:@"com.facebook.react.%sQueue", moduleName];
+      methodQueue = dispatch_queue_create(methodQueueName.UTF8String, DISPATCH_QUEUE_SERIAL);
+    }
 
     if (moduleHasMethodQueueGetter) {
       /**