avrcp_target: return value and code clean up

avrcp: use PANEL as default unit + subunit info

avrcp_target: return unused fields in subunit_info as 0xff

Remove stdio.h include from btstack_debug.h, add to individual files

avrcp: fix compile

avrcp: add all operation IDs, accept all valid operation IDs

avrcp_target: fix subunit info response

avoid #include "btstack.h" by core stack

avrcp_target: emit operation button release event

avrcp: new field button_pressed in AVRCP_SUBEVENT_OPERATION

avrcp_target: fix notification changed event

avrcp_target: fix command handling (regression from 9970238)

avrcp_target: fix command handling (regression from 9970238)

avrcp_target: remove unused functions

avrcp: avoid out of bound reads in target and controller

avrcp_target: mark supported events and companies as const

avrcp: request can send now again for controller if both want to send

avrcp: support de-init

# Conflicts:
# src/classic/avrcp_target.h

avrcp_target: avoid warning without bstack_assert

avrcp_target: fix compile warning using invalid pointers in memcpy with len == 0

avrcp_controller: rename transaction_label

avrcp: check packet type and return if fragmented (currently not supported)

test/fuzz: prepare for avrcp fuzzing

avrcp: use defines instead of enum for features

avrcp: replacle if-else-chain with simple if + return