Expose RuntimeExecutor on CatalystInstance (#28851)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/28851

This diff creates a RuntimeExecutor that uses the bridge and exposes it on CatalystInstanceImpl.

Changelog: [Internal]

Reviewed By: mdvacca, RSNara

Differential Revision: D21051949

fbshipit-source-id: b3977fc14fa19089f33e297d29cedba0d067526d

ReactAndroid/src/main/java/com/facebook/react/bridge/CatalystInstance.java

@@ -99,14 +99,18 @@ public interface CatalystInstance
   void setGlobalVariable(String propName, String jsonValue);
 
   /**
-   * Get the C pointer (as a long) to the JavaScriptCore context associated with this instance.
+   * Do not use this anymore. Use {@link #getRuntimeExecutor()} instead. Get the C pointer (as a
+   * long) to the JavaScriptCore context associated with this instance.
    *
    * <p>Use the following pattern to ensure that the JS context is not cleared while you are using
    * it: JavaScriptContextHolder jsContext = reactContext.getJavaScriptContextHolder()
    * synchronized(jsContext) { nativeThingNeedingJsContext(jsContext.get()); }
    */
+  @Deprecated
   JavaScriptContextHolder getJavaScriptContextHolder();
 
+  RuntimeExecutor getRuntimeExecutor();
+
   void addJSIModules(List<JSIModuleSpec> jsiModules);
 
   /**

ReactAndroid/src/main/java/com/facebook/react/bridge/CatalystInstanceImpl.java

@@ -664,6 +664,9 @@ public class CatalystInstanceImpl implements CatalystInstance {
     return mJavaScriptContextHolder;
   }
 
+  @Override
+  public native RuntimeExecutor getRuntimeExecutor();
+
   @Override
   public void addJSIModules(List<JSIModuleSpec> jsiModules) {
     mJSIModuleRegistry.registerModules(jsiModules);