Allow selecting bluetooth profile and codecs

[brodock]

Problem

Bluetooth audio in Linux is horrible in general. The reason are many, but goes from poorly implemented HSP/HSF support to poorly implemented A2DP support.

More recently, pulseaudio fixed A2DP part with a series of (heated) MR and changes. The TL;DR is that in Pulseaudio 15.x when you are using A2DP you can now select codecs like AptX LDAC and AAC. That allows people using headphones from the last 5 years to actually sound good.

The problem is that this is not automatically set, and requires dealing with a new interface (PulseAudio's Messaging API).

Relevant links:

• Original MR (with drama and context): https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/227
• Follow up MR (with less drama, that got merged): https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/440
• The messaging API: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/51
• The change that moved messaging API to use JSON: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/525
• Pipewire related issue tracking Pulseaudio work: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/348
• Pavucontrol code that handles switching code: https://gitlab.freedesktop.org/pulseaudio/pavucontrol/-/merge_requests/54

Proposal

I understand that selecting a profile and codecs is not the greatest of the UX, but currently there is no good heuristic on how to do that automatically. So as an interation over what we have today (poor audio that user can't fix), I believe we should allow the user to select both the profile and the codec.

And because this requires pulseaudio 15 to work, that means we would also need to backport that :)

Prior Art

This is how pavucontrol handles it (link to the source above in relevant links):