Wire up configuration to use microtasks in RuntimeScheduler, Hermes and React (#41090)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41090

This propagates to enable the use of microtasks in the React reconciler, Runtime Scheduler and Hermes.

Changelog: [internal]

Reviewed By: sammy-SC

Differential Revision: D50177355

fbshipit-source-id: 6cf23cf72b63d19f50453d3e4cc4ac1b056dbd92

packages/react-native/ReactCommon/react/renderer/scheduler/Scheduler.cpp

@@ -139,6 +139,14 @@ Scheduler::Scheduler(
   reduceDeleteCreateMutationLayoutAnimation_ = true;
 #endif
 
+#ifdef ANDROID
+  CoreFeatures::enableMicrotasks =
+      reactNativeConfig_->getBool("react_fabric:enable_microtasks_android");
+#else
+  CoreFeatures::enableMicrotasks =
+      reactNativeConfig_->getBool("react_fabric:enable_microtasks_ios");
+#endif
+
   CoreFeatures::blockPaintForUseLayoutEffect = reactNativeConfig_->getBool(
       "react_fabric:block_paint_for_use_layout_effect");
 

packages/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp

@@ -105,6 +105,17 @@ std::unique_ptr<jsi::Runtime> HermesInstance::createJSRuntime(
   auto heapSizeMB = heapSizeConfig > 0
       ? static_cast<::hermes::vm::gcheapsize_t>(heapSizeConfig)
       : 3072;
+
+#ifdef ANDROID
+  bool enableMicrotasks = reactNativeConfig
+      ? reactNativeConfig->getBool("react_fabric:enable_microtasks_android")
+      : false;
+#else
+  bool enableMicrotasks = reactNativeConfig
+      ? reactNativeConfig->getBool("react_fabric:enable_microtasks_ios")
+      : false;
+#endif
+
   ::hermes::vm::RuntimeConfig::Builder runtimeConfigBuilder =
       ::hermes::vm::RuntimeConfig::Builder()
           .withGCConfig(::hermes::vm::GCConfig::Builder()
@@ -119,6 +130,7 @@ std::unique_ptr<jsi::Runtime> HermesInstance::createJSRuntime(
                             .build())
           .withES6Proxy(false)
           .withEnableSampleProfiling(true)
+          .withMicrotaskQueue(enableMicrotasks)
           .withVMExperimentFlags(vmExperimentFlags);
 
   if (cm) {