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

Summary:
Issues: Related to  #13439
react-native-website:Related to PR [#792](facebook/react-native-website#792)
solution: #13439 (comment)

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: #23336

Differential Revision: D14298654

Pulled By: cpojer

fbshipit-source-id: 5cc17539a51154faeb838349b068d92511946f79

Author: RoJoHub

ReactAndroid/src/androidTest/java/com/facebook/react/testing/ReactAppTestActivity.java

@@ -213,6 +213,14 @@ public void loadBundle(final ReactInstanceSpecForTest spec, String bundleName, b
     } else {
       builder.addPackage(new MainReactPackage());
     }
+    /**
+     *  The {@link ReactContext#mCurrentActivity} never to be set if initial lifecycle state is resumed.
+     *  So we should call {@link ReactInstanceManagerBuilder#setCurrentActivity}.
+     *
+     *  Finally,{@link ReactInstanceManagerBuilder#build()} will create instance of {@link ReactInstanceManager}.
+     *  And also will set {@link ReactContext#mCurrentActivity}.
+     */
+    builder.setCurrentActivity(this);
     builder
         .addPackage(new InstanceSpecForTestPackage(spec))
         // By not setting a JS module name, we force the bundle to be always loaded from

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

@@ -246,6 +246,12 @@ public ReactInstanceManager build() {
       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");