floss: avrcp: have floss respond to additional APIs

Let Floss respond to Get Media Player and Get Now Playing List
requests. The former is required to allow the AVRCP init process to
complete between target and control. Moreover, the latter is required
because not all peripherals fetch the media metadata through Get
Element Attributes; many get such information through the Track Changed
Notification.

Bug: 259144894
Tag: #floss
Test: bluetooth_AdapterAUHealth.au_avrcp_media_info_test.floss
BYPASS_LONG_LINES_REASON: Bluetooth likes 120 lines

Change-Id: Ia35e0ade40a92ae0a5ed1019f24d8551110dcc93