Add AudioSource.latency

[ACrazyTown]

This PR adds a latency field to AudioSource that returns the estimated playback latency of the sound.

On native targets (that use OpenAL Soft) the same method from #1759 is used, although exposing it as a seperate field instead of applying it directly to the sound's time.

HTML5 uses AudioContext.baseLatency and AudioContext.outputLatency

In the case where it's not possible to query the playback latency (eg. Flash) 0 is returned.

[mcagabe19]

iOS will give null since it uses mojoal instead if OpenAL SOFT.

[MAJigsaw77]

iOS will give null since it uses mojoal instead if OpenAL SOFT.

@ACrazyTown Since some platforms might use mojoAl or something else for example, I'd suggest checking if the extension is supported first AL.isExtensionPresent("AL_SOFT_source_latency").

[ACrazyTown]

@mcagabe19 @MAJigsaw77 The native C++ functions will return null if LIME_OPENALSOFT is not defined. This is later checked on the Haxe side:

lime/src/lime/_internal/backend/native/NativeAudioSource.hx

Lines 592 to 599 in 3f9041a

	public function getLatency():Float
	{
	var offsets = AL.getSourcedvSOFT(handle, AL.SEC_OFFSET_LATENCY_SOFT, 2);
	if (offsets != null)
	return offsets[1] * 1000;
	return 0;
	}

Is that not enough?

[MAJigsaw77]

@mcagabe19 @MAJigsaw77 The native C++ functions will return null if LIME_OPENALSOFT is not defined. This is later checked on the Haxe side:

lime/src/lime/_internal/backend/native/NativeAudioSource.hx

Lines 592 to 599 in 3f9041a

	public function getLatency():Float
	{
	var offsets = AL.getSourcedvSOFT(handle, AL.SEC_OFFSET_LATENCY_SOFT, 2);
	if (offsets != null)
	return offsets[1] * 1000;
	return 0;
	}

Is that not enough?

It's not because openal soft can be there, but the platform might not support latency, in any case that check should make it fine if added.