TM iOS: Use weak_ptr to pass around Instance to avoid unreleased refs

Summary:
There is a timing issue when reloading the bridge (in dev mode) and the tear down of the TurboModules. This causes `Instance` to never get freed, hence the "bridge" isn't cleaning up properly. The side effect can be bogus error saying that it's unable to find a module.

To address this, JSCallInvoker should just take in weak_ptr<Instance>.

Reviewed By: RSNara

Differential Revision: D14739181

fbshipit-source-id: f9f2a55486debaeb28d3d293df3cf1d3f6b9a031

React/CxxBridge/RCTCxxBridge.mm

@@ -210,7 +210,7 @@ struct RCTInstanceCallback : public InstanceCallback {
   return _jsMessageThread;
 }
 
-- (std::shared_ptr<Instance>)reactInstance
+- (std::weak_ptr<Instance>)reactInstance
 {
   return _reactInstance;
 }

ReactCommon/turbomodule/core/JSCallInvoker.cpp

@@ -12,14 +12,15 @@
 namespace facebook {
 namespace react {
 
-JSCallInvoker::JSCallInvoker(std::shared_ptr<Instance> reactInstance)
+JSCallInvoker::JSCallInvoker(std::weak_ptr<Instance> reactInstance)
   : reactInstance_(reactInstance) {}
 
 void JSCallInvoker::invokeAsync(std::function<void()>&& func) {
-  if (reactInstance_ == nullptr) {
+  auto instance = reactInstance_.lock();
+  if (instance == nullptr) {
     return;
   }
-  reactInstance_->invokeAsync(std::move(func));
+  instance->invokeAsync(std::move(func));
 }
 
 } // namespace react

ReactCommon/turbomodule/core/JSCallInvoker.h

@@ -26,13 +26,13 @@ class Instance;
  */
 class JSCallInvoker {
 public:
-  JSCallInvoker(std::shared_ptr<Instance> reactInstance);
+  JSCallInvoker(std::weak_ptr<Instance> reactInstance);
 
   void invokeAsync(std::function<void()>&& func);
   // TODO: add sync support
 
 private:
-  std::shared_ptr<Instance> reactInstance_;
+  std::weak_ptr<Instance> reactInstance_;
 };
 
 } // namespace react

ReactCommon/turbomodule/core/platform/ios/RCTTurboModule.h

@@ -91,6 +91,6 @@ private:
 @interface RCTBridge ()
 
 - (std::shared_ptr<facebook::react::MessageQueueThread>)jsMessageThread;
-- (std::shared_ptr<facebook::react::Instance>)reactInstance;
+- (std::weak_ptr<facebook::react::Instance>)reactInstance;
 
 @end