bluetooth: Add currently active codec name to card/sink/source proplist

bluetooth: Add currently active codec name to card/sink/source proplist

This exposes the currently active codec on the source or sink via the
proplist and can be seen in output of pacmd list-sinks/list-sources.
Also set it on the card. In case of a bi-directional codec, the codec
for the sink and source could be different. For example, for aptX-LL,
the codec name on card, sink and source would be aptx-ll, aptx and sbc
respectively.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/440>