[bt][avrcp] Initial AVCTP and AV/C crate

Design heavily influenced by AVDTP crate.

Supports:

- Owning a L2CAP socket to a remote peer.
- Responding to unit info and subunit commands.
- Sending AVC passthrough commands to a target.
- Receving target passthrough and vendor dependent packets.
- Sending responses back to controller commands.

BT-657
Test: fx run-test bt-avctp-tests

Change-Id: I861d86a61f17294c430beecf0ca08cea3264e5ea