Pref Sound: auto select free device channels

[ronso0]

I started another coffee break project to add little helper:
when you need to configure multiple sound outputs using one device, like channels 1-2 for Main & 3-4 for headphones as with many controller soundcards, and you configured the first output it is very pleasant if the next free channel pair is selected automatically for the second output.

1. Main: select device XY -> channels 1-2 selected (default from populating the channels box)
2. Headphones: select device XY -> channels 3-4 are selected automatically

That saves one click (yeaiiy!!), but more importantly: it avoids mis(re-)configuration in the Heat of the Night:tm: (assign same channels twice, Apply, error, meeeh, select correct channels, Apply).

Note: this does just combobox index matching, i.e. does not check channel overlap like
Mic1: channel 1, Aux1: channels 1-2.

Closes #10163

This is still WIP but it's working nicely already.
I'll do more testing and polish it.

• remove DEBUG commit

[fwcd]

I like this, it makes the common case very convenient, though I think it could also feel a bit "magical", especially if the user has a more esoteric device/channel configuration.

[ronso0]

Thanks for testing this!
I rarely use more than one IO device so real-world examples that are can be improved are welcome!

Note that the occupied channel indices are stored per device so it won't suggest weird channels for formerly unconfigured devices.
If for example a user first selected channels 3/4 and selects the same device again it'll select 1/2 as before, like for all formerly unused devices. Can't think of an example case where the auto-select would be disturbing, or more inconvenient than the current behaviour.
For scenarios where muliple mono channels are configured for a device, auto-select pick 1/2 but this is also the current behaviour. Making auto-select pick another mono channel is doable but I'm not sure it's desireable in all cases.

[ronso0]

It's working nicely, didn't encounter any hickups, incl. Query Devices.

Ready for review.

[ronso0]

bump
Is there anything left to do?

[ronso0]

ba-bump

[JoergAtGithub]

Just tested this and it works very neat with my Traktor Z2 (2xOut Ch + 4x In Ch in unusual order) accross all the Windows Audio driver APIs.
Please fix the conflict.

[ronso0]

Thanks for your review @JoergAtGithub !
Ready for merge.

[JoergAtGithub]

LGTM! Thank you!