Add support for using an Android Service to host the Godot engine

- Provide a `GodotService` Android service implementation which can be used to host an instance of the Godot engine
- Provide a `RemoteGodotFragment` Android fragment implementation which provides the view and logic to wrap connection to a `GodotService` instance

platform/android/java/app/build.gradle

@@ -208,7 +208,9 @@ android {
     flavorDimensions 'edition'
 
     productFlavors {
-        standard {}
+        standard {
+            getIsDefault().set(true)
+        }
         mono {}
     }
 

platform/android/java/app/src/com/godot/game/GodotApp.java

@@ -37,8 +37,6 @@ import android.util.Log;
 
 import androidx.core.splashscreen.SplashScreen;
 
-import com.godot.game.BuildConfig;
-
 /**
  * Template activity for Godot Android builds.
  * Feel free to extend and modify this class for your custom logic.