Add a --audio-output-latency command-line argument

This allows optimizing the audio output latency on higher-end CPUs,
especially in projects that do not expose a way to override this setting.

drivers/alsa/audio_driver_alsa.cpp

@@ -111,7 +111,7 @@ Error AudioDriverALSA::init_output_device() {
 	// In ALSA the period size seems to be the one that will determine the actual latency
 	// Ref: https://www.alsa-project.org/main/index.php/FramesPeriods
 	unsigned int periods = 2;
-	int latency = GLOBAL_GET("audio/driver/output_latency");
+	int latency = Engine::get_singleton()->get_audio_output_latency();
 	buffer_frames = closest_power_of_2(latency * mix_rate / 1000);
 	buffer_size = buffer_frames * periods;
 	period_size = buffer_frames;