AVRCP: Fix get metadata attribute responses

* Add checks for remaining buffer capacity to handle long metadata
* Change the attribute number max to AVRC_MAX_NUM_MEDIA_ATTR_ID
* Consolidate attribute value filling code between GetElementAttributes
  and GetItemAttributes
* Check requested media attribute IDs before building response

Bug: 32407250, 33001066
Test: manual - connect to carkit and play music, see metadata and hear audio
Change-Id: I8f0c47148be35100202398c754861abb1fb9def1