Remove java and UnityPlayer changes to the windowmanager so it can be…

[thomas-stockx]

… fully handled by Flutter

For rendering full screen Unity with Flutter widgets on top:

return Scaffold(
  body: Stack(
  children: <Widget>[
    UnityWidget(
      onUnityViewCreated: onUnityCreated,
    ),
    Positioned(
       /// ...

For rendering a flutter app with a Unity widget inside:

return Scaffold(
  appBar: AppBar(
    title: Text('Title'),
  ),
  body: Stack(
    children: <Widget>[
      Center(
        child: SizedBox(
          height: 300,
          width: 300,
          child: UnityWidget(
            onUnityViewCreated: onUnityCreated,
          ),
        ),
      ),
      Positioned(
        /// ...

This change fixes the status bar overlapping with the AppBar.

[juicycleff]

Thanks, @thomas-stockx I had plans fixing all these when I get the time, but so far you have been actively working on it. Promise to be back fully once I am done with my project, which should be soon