Use only PCM as the media feeding format

* Removed field tA2D_AV_MEDIA_FEEDINGS.format, because we always
  use/assume the feeding format is PCM.
* Removed tA2D_AV_MEDIA_FEED_CFG_PCM, tA2D_AV_MEDIA_FEED_CFG,
  tA2D_AV_CODEC_PCM, and tA2D_AV_CODEC_NONE, because they are not
  needed/used anymore.
* Removed feeding mode:
  - tBTIF_MEDIA_INIT_AUDIO_FEEDING.feeding_mode
  - tBTIF_AV_FEEDING_MODE, BTIF_AV_FEEDING_ASYNCHRONOUS,
    BTIF_AV_FEEDING_SYNCHRONOUS
  - tBTIF_MEDIA_CB.feeding_mode
* Added new APIs and the corresponding unit tests:
  - A2D_CodecConfigMatchesCapabilities()
  - A2D_BuildSinkConfig()
  - A2D_CodecEquals()
  - A2D_CodecRequiresReconfig()

Also:
 * Removed header file btif/include/btif_av_api.h because it is not
   needed anymore.
 * Removed functions or typedefs that are unused or replaced:
   - bta_av_co_audio_codec_match() -> replaced by
     A2D_CodecConfigMatchesCapabilities()
   - bta_av_co_audio_codec_cfg_matches_caps()
   - bta_av_co_audio_peer_reset_config()
   - bta_av_co_audio_discard_config()
   - bta_av_co_get_codec_info()
   - bta_av_co_peer_cp_supported()
   - tA2D_AV_CODEC_ID
   - tBTIF_AV_CODEC_INFO
 * Increased the sampling_freq storage from uint16_t to uint32_t
 * Decreased the number of channels n_channels storage from uint16_t
   to uint8_t
 * Removed unneessary global function declarations inside btif_av_co.h
 * Changed the order of the A2D_BuildSrc2SinkConfig() arguments, so
   the order is more intuitive.
 * Misc other cleanup:
   - file bta_av_co.cc: code simplification, renamed snk -> sink,
     Removed unnecessary cast-away of a const argument: bta_av_co_cp_scmst
     Renamed/updated bta_av_co_audio_peer_supports_codec() ->
             bta_av_co_find_peer_sink_supports_codec()
     Renamed/updated bta_av_co_audio_peer_src_supports_codec() ->
             bta_av_co_find_peer_src_supports_codec()

Bug: 30958229
Test: A2DP tested manually. Unit tests included in the CL.
Change-Id: I60981c62b1a88491b5232c4f6515933c4261fac9