[AUDIO_WORKLET] Add multichannel audio tests. NFC

[cwoffenden]

These are the audio worklet tests from #22753 extracted to a standalone PR. The tests are:

• Multiple stereo inputs mixing in the processor to a single stereo output
• Multiple stereo inputs copying in the processor to multiple stereo outputs
• Multiple mono inputs mixing in the processor to a single mono output
• Multiple mono inputs copying in the processor to L+R stereo outputs

The tests use different stack sizes (from 2kB to 6kB depending on the requirement).

The audio tracks were composed by Tim Wright especially for Emscripten and released under a CC0 license.

The tests can be run manually via:

test/runner interactive.test_audio_worklet_stereo_io
test/runner interactive.test_audio_worklet_2x_stereo_io
test/runner interactive.test_audio_worklet_mono_io
test/runner interactive.test_audio_worklet_2x_hard_pan_io

There are no code changes to Emscripten apart from integrating the test.

[sbc100]

I love that Tim Wright composed our audio tests :) Please tell him I was a great fan or Lemmings and Shadow of the Beast 2 back in the day.

[cwoffenden]

I love that Tim Wright composed our audio tests :)

😁

Please tell him I was a great fan or Lemmings and Shadow of the Beast 2 back in the day.

Now we'll need to widen the office doors even more to let in his ego!

[sbc100]

Why are these two JS functions needed? Is this functionality not available though existing emscripten APIs?

Are folks expected to create their own audio elements like this?

[cwoffenden]

Yep, there's no provision (that I know of) to create audio tracks.

In reality the audio will probably come in via other means (we decode and mix Opus files, for example, or generate effects).

[sbc100]

I wish I knew the audio worklet API better so I could give this a better review myself.

@juj perhaps you could review later if you get time?

lgtm to all the parts I could understand