Initial implementation of requestIdleCallback on Android

Summary:
This is a follow up of the work by brentvatne in #5052. This addresses the feedback by astreet.

- Uses ReactChoreographer with a new callback type
- Callback dispatch logic moved to JS
- Only calls into JS when needed, when there are pending callbacks, it even removes the Choreographer listener when no JS context listen for idle events.

** Test plan **
Tested by running a background task that burns all remaining idle time (see new UIExplorer example) and made sure that UI and JS fps stayed near 60 on a real device (Nexus 6) with dev mode disabled. Also tried adding a JS driven animation and it stayed smooth.

Tested that native only calls into JS when there are pending idle callbacks.

Also tested that timers are executed before idle callback.
```
requestIdleCallback(() => console.log(1));
setTimeout(() => console.log(2), 100);
burnCPU(1000);
// 2
// 1
```

I did *not* test with webworkers but it should work as I'm using executor tokens.
Closes https://github.com/facebook/react-native/pull/8569

Differential Revision: D3558869

Pulled By: astreet

fbshipit-source-id: 61fa82eb26001d2b8c2ea69c35bf3eb5ce5454ba

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -32,7 +32,7 @@ import com.facebook.react.uimanager.UIImplementationProvider;
 import com.facebook.react.uimanager.ViewManager;
 
 /**
- * This class is managing instances of {@link CatalystInstance}. It expose a way to configure
+ * This class is managing instances of {@link CatalystInstance}. It exposes a way to configure
  * catalyst instance using {@link ReactPackage} and keeps track of the lifecycle of that
  * instance. It also sets up connection between the instance and developers support functionality
  * of the framework.