preferreddevice: Always prefer the default device

Oliver Beardrequested to merge
work/olib-tp/default-preferred into master

Otherwise, a new default device which is suspended (like bluetooth earphones) is unexpectedly ignored.

The class is changed from a more heavy construction around the default sink/source in pulseaudio-qt to just a simple wrapper. It is still necessary because QML also wants to know the preferred device, otherwise it could be removed entirely.

Marked as draft as the consequences of this should be fully considered, and because we can probably clean up code further if we like the solution.

What this intends to address is an issue where, on connecting bluetooth earphones, they become the default device, but the preferred device (i.e. as far as kded/applet cares) remains as, say, speakers, until the bluetooth earphones are unsuspended and brought to playing status. It seems obvious to me that they are default, they are where audio will play, so they are preferred.

No KDE BUG exists.

CC: @drosca (original implementation) @sitter (moving this out of pulseaudio-qt) @davidedmundson

Edited by Oliver Beard

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