Check if mCurrentActivity is set according to LifecycleState (#23336)

Summary:
Issues: Related to  #13439
react-native-website:Related to PR [#792](https://github.com/facebook/react-native-website/pull/792)
solution: https://github.com/facebook/react-native/issues/13439#issuecomment-400256114

When we integration with Existing  Android Apps.and set LifecycleState  is `LifecycleState.RESUMED`.
It's lead to `mCurrentActivity`  is null .

At this time , the behave of set `mCurrentActivity ` which  is unexpectedly.

## Changelog
[Android] [Fixed] - Check if mCurrentActivity is set according to LifecycleState
Pull Request resolved: https://github.com/facebook/react-native/pull/23336

Differential Revision: D14298654

Pulled By: cpojer

fbshipit-source-id: 5cc17539a51154faeb838349b068d92511946f79

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

@@ -246,6 +246,12 @@ public class ReactInstanceManagerBuilder {
       mApplication,
       "Application property has not been set with this builder");
 
+    if (mInitialLifecycleState == LifecycleState.RESUMED) {
+      Assertions.assertNotNull(
+        mCurrentActivity,
+        "Activity needs to be set if initial lifecycle state is resumed");
+    }
+
     Assertions.assertCondition(
       mUseDeveloperSupport || mJSBundleAssetUrl != null || mJSBundleLoader != null,
       "JS Bundle File or Asset URL has to be provided when dev support is disabled");