leaudio: Fix handling AvailableContext changes during streaming.

As per specification, when Unicast Acceptor accepts stream with given
context type and later remove accepted Context Type from the Available
Context Types, the Unicast Initiator should not close the stream.

Above can be found in CAP 1.0.1, 7.1.1. Available Audio Contexts.

Ideal behavior of Unicast Acceptor would be to keep Available Context
per each connected device and notify about removed context only devices
which are not streaming yet.
In the real life, there are many devices out there which keeps global
Available Context Type value and just use it for all the Unicast Client.

This behavior cause troubles for Unicast Clients, expecialy when during
the streaming, one of the set member disconnects and later reconnects.

Android keeps available context type per each device and also keeps
context types in the group trying to remember what context types where
accepted during the stream creation. Unfortunatelly this approach has an
issue especially when one set member disconnects and reconnects.

With new approach, Android keeps streaming context types in the group
and whenever group->GetAvailableContext() is called, it ORs Available
Contexts from all the ASEs with currently Streaming Contexts.

Bug: 396312681
Test: atest bluetooth_le_audio_test bluetooth_le_audio_client_test
Test: manual test cases with recording, disable/enable 1 set member
Flag: Exempt, day-to-day fix, regression verified with unit tests and QA
Change-Id: Ib328d417498fe3f1ac65f07b7df77ff58c646063