audio: Fix BT AIDL HAL module implementation

In order to align with legacy behavior, when opening a stream,
the module must suggest the current configuration of the BT session.
For that to work, the BT device proxy must be opened prior
to creating a stream, code moved to ModuleBluetooth.

Fix minor inconsistencies and bugs found during testing.

Bug: 301213930
Bug: 316027906
Test: atest pts-bot
Change-Id: I04ddaf73be82f872a3f32a789563c3cbd648eb61