Execute task.main on the UI thread when possible

Property definitions

android $ NativeActivity :: run_on_ui_thread
	# Execute `task.main` on the UI thread when possible
	fun run_on_ui_thread(task: Task) import Task.main in "Java" `{
		final nit.app.NitObject final_task = task;
		Runnable runnable = new Runnable() {
			@Override
			public void run() {
				Task_main(final_task);
			}
		};
		self.runOnUiThread(runnable);
	`}
lib/android/activities.nit:44,2--54,3