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_godot_wrapper.h

@@ -42,9 +42,7 @@
 class GodotJavaWrapper {
 private:
 	jobject godot_instance;
-	jobject activity;
 	jclass godot_class;
-	jclass activity_class;
 
 	GodotJavaViewWrapper *godot_view = nullptr;
 
@@ -84,9 +82,10 @@ private:
 	jmethodID _enable_immersive_mode = nullptr;
 	jmethodID _is_in_immersive_mode = nullptr;
 	jmethodID _on_editor_workspace_selected = nullptr;
+	jmethodID _get_activity = nullptr;
 
 public:
-	GodotJavaWrapper(JNIEnv *p_env, jobject p_activity, jobject p_godot_instance);
+	GodotJavaWrapper(JNIEnv *p_env, jobject p_godot_instance);
 	~GodotJavaWrapper();
 
 	jobject get_activity();