Add Packet class as alternative to BT_HDR

Adds Packets, Iterators, and Packet Builders to Bluetooth to be used as
an alternative to BT_HDR.

 - Packet is a base class used to pass around data. It is intended to be
   immutable after creation and subclasses will implement all required
   functions and their own accessor methods to retrieve data.

 - Iterator provides a convienent way to traverse packet data.

 - PacketBuilder is used to construct Packets. This class is should be
   the only way to mutate packet objects.

Also add class representations for the following packet types:
  AVRCP (Base Packet)
    AVRCP Vendor Packet
      AVRCP Get Capabilities Packet
      AVRCP Get Element Attributes Packet
      AVRCP Register Notification Packet
      AVRCP Get Play Status Packet
      AVRCP Reject Packet
    AVRCP Pass Through Packet

Adds net_test_btpackets to run_host_unit_tests.py for pre-submit

Bug: 68854188
Test: run host native test net_test_packets
Change-Id: I0d385710178e5feb2d5089847580754ad6308709