pandora: add support to VCP tests

Implements VCP tests that are supported by bluetooth stack. Tests
that are skipped require mechanism to trigger sending write to Volume
Control Point with "Unmute" OP code

Bug: 369938109
Flag: TEST_ONLY
Test: atest pts-bot:VCP -v
Change-Id: I1fa01b7e184abe164da0420a70c46b4c1c2fb75d