[Android] Support immersive fullscreen mode for LaunchScreen

For Android version >=KikKat, fullscreen mode should be immersive fullscreen mode.

BUG=XWALK-1593
The code is in core internal so you need to consider any case that how embedder possibly using it. However, embedding api is not supporting launchscreen well for now. But it's always good to consider for future.

And the discussion reminds me that, here you shouldn't justify whether the activity is fullscreen. Instead, you could apply both the `SystemUiVisibility` and `window.flags` of the App's Activity to the launch screen will pop up.