Add loop_mode to AudioStreamPlayer & AudioStreamPlayback

[Mickeon]

Implements godotengine/godot-proposals#3120, (minus actually stripping the import)

This PR implemets loop_mode for AudioStreamPlayer, AudioStreamPlayer2D, AudioStreamPlayer3D and AudioStreamPlayback.

This allows changing the looping mode of the AudioStream, regardless of how it was imported, even as the stream is playing, which leads to pretty interesting results! Imagine playing a sound, keep it looping continuously, until a key is released.

AudioStreamPlayer.loop.mode.mp4

By default, for the AudioStreamPlayer's, this property is set to "Detect", which lets any generated AudioStreamPlayback automatically figure out the loop_mode, based on their respective AudioStream Resource.

Note is that, the streams may vary a lot (MP3, Ogg, WAV...). Their implementation has been mostly unchanged in this PR, so it is not guaranteed that the given loop_mode is supported, if at all, in fact. Whenever this is the case, a warning configuration is issued. When actually playing the AudioStream with AudioStreamPlayback, the variable is internally reassigned to its closest equivalent and a warning is sent to the console (this has been configured manually).

Configuration Warning	Console Warning

The way AudioStreams are imported into the editor is left unchanged. This feature is all on top of it.

What I would like to do:

• Fix AudioStreamPlaybackWAV not resuming forward as expected after switching from Ping Pong/Backward to Forward (as if stuck looping backwards).
• Hide unsupported Loop Modes from selection when the AudioStream of AudioStreamPlayer does not support them (I believe validate_property() allows you to do this). PROPERTY_TYPE_ENUM does not support skipping options (adding that to my list, I suppose). The closest thing is a reminder next to each option.
• Move LoopMode::DETECT to the top of the enum.
• Manage detecting unsupported loop modes outside of AudioStreamPlayback, and into AudioStreamPlayer (Have AudioStream return a list of supported modes).
• Clean-up this code considerably.
• Add and update the documentation.

Optional ideas:

• Default most AudioStreamPlaybacks created with AudioStream.instantiate_playback() to LoopMode.DETECT.
• Expose virtual _set_loop_mode() and _get_unsupported_loop_modes() methods to GDScript.
• Allow overriding loop_begin and loop_end (if supported).
• Remove (now) unnecessary enum from AudioStreamWAV (the only AudioStream that supports all modes).
• Move the LoopMode enum to AudioStreamPlayer itself(?).

Feedback is absolutely appreciated.
I am particularly concerned about the naming. Perhaps it should be called loop_mode_override, or something along those lines in the AudioStreamPlayers. Or playback_mode (renaming the constants accordingly, too) because that's technically what it is, actually? I was getting confused a bit while working on it,

[Mickeon]

Previews are outdated. The property has been shifted higher up and its group has been removed (no point having it if overriding loop_begin and loop_end isn't supported). However, it's undeniable that all of these properties require some form of grouping around.

[Mickeon]

The PR is now functional enough to be reviewed!

[akien-mga]

We discussed it briefly in a PR review meeting, there was no clear consensus in favor of exposing this this way. This should be rediscussed for a future release together with the interactive music enhancements that could also include easier configuration of sample looping.

[fguillen]

Wondering if there has been any update on this.

[Calinou]

Wondering if there has been any update on this.

The above comment is still relevant. Akien is referring to #64488 which hasn't been merged yet (and won't be for 4.1, as it requires further work).

[Mupli]

any news on Loops?

[Mickeon]

Nothing has been recently talked about on this regard. Judging by the last PR review meeting, this is not the maintainers want this feature to be accessed.

[LEEROY-3]

I apologize, but what exactly is being discussed by the team for so long? It has been over a year since this PR is functional and it is a pretty simplistic feature. It's unfortunate that this engine still doesn't allow easily overriding loop mode via player.

I would greatly appreciate if you shared some of the concerns the team had with this particular PR.

[akien-mga]

Superseded by #86473.