On platform release T, the legacy `audio.a2dp.default` HAL no longer
exists, and cannot be trivially restored for generic system-side A2DP
audio support. Rather than trying to cling on to its existence (which
does not even work anymore even if one did so), it is time to come up
with a new solution.
This commit introduces a system-side implementation of the generic
bluetooth audio HAL. The HAL itself is modelled after the default
bluetooth audio HAL, while substantial components of the default audio
HAL are also included as it has to also implement the audio HAL
interfaces.
The audio HAL implementation is delegated to `audio.sysbta.default`,
forked from `audio.bluetooth.default` from the Bluetooth apex package.
It then communicates with the bluetooth audio HAL interfaces, which need
to live in the same process (in this case, the process of the sysbta
HAL). This is why we cannot just load `audio.sysbta.default` into the
default audio HAL or the audioserver process directly, but rather have
to include our own simplistic audio HAL implementation.
For now, the audio HAL implementation only includes one for the 6.0
version, but technically, an interface for *every* audio HAL version
needs to exist. This, along with other messiness in the sysbta
implementation, will be addressed in a future commit.
Note that to actually make use of the sysbta audio hal, patches in
frameworks/av and packages/modules/Bluetooth are required to introduce
support for the property `persist.bluetooth.system_audio_hal.enabled`.
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