Use RuntimeConfig for microtasks

Summary:
Changelog:
[general][change] - Use RuntimeConfig instead of VM Experiment Flag to set up the micro task queue.

Reviewed By: neildhar

Differential Revision: D37353947

fbshipit-source-id: 5c8f35c0a79d70cb0d234e881e55058cffb44ac8

Author: Michael Anthony Leon

ReactCommon/react/bridging/tests/BridgingTest.h

@@ -38,7 +38,7 @@ class BridgingTest : public ::testing::Test {
         runtime(hermes::makeHermesRuntime(
             ::hermes::vm::RuntimeConfig::Builder()
                 // Make promises work with Hermes microtasks.
-                .withVMExperimentFlags(1 << 14 /* JobQueue */)
+                .withMicrotaskQueue(true)
                 .build())),
         rt(*runtime) {}