Apply playback speed selection

 - Add Settings UI
 - Remove unnecessary values related to Full Mode
 - Remove unnecessary hierarchy in list item layout
 - Enable to select Playback Speed in Settings

Also changes:
   Keep Fullscreen UI when window focus changed in demo app

PiperOrigin-RevId: 295655858

constants.gradle

-// Copyright (C) 2017 The Android Open Source Project
+// Copyright 2017 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.