Ogg VorbisComment should allow both COMMENT and DESCRIPTION fields

[StefanBruens]

Summary of the bug:

Although there are only 15 standard field names for metadata (​http://xiph.org/vorbis/doc/v-comment.html), there is nothing which forbids e.g. COMMENT as a field name.

Notably ​https://wiki.xiph.org/Field_names links an Excel sheet with several additional fields, including COMMENT.

​https://wiki.xiph.org/VorbisComment also links to pages listing several other common field names.

Unfortunately ffmpeg maps the COMMENT field to DESCRIPTION, although both should be distinct:

​https://github.com/FFmpeg/FFmpeg/blob/fa81de4af045317aefeae941cf54f349c39e81e0/libavformat/vorbiscomment.c#L37

How to reproduce:

% ffmpeg -i input.oga -acodec copy -metadata:s:a COMMENT=MyComment output.oga

% ffprobe output.oga | grep MyComment
DESCRIPTION: MyComment

ffmpeg version 6.0 Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 13 (SUSE Linux)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --incdir=/usr/include/ffmpeg --extra-cflags='-O2 -Wall -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -ffat-lto-objects -g' --optflags='-O2 -Wall -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -ffat-lto-objects -g' --disable-htmlpages --enable-pic --disable-stripping --enable-shared --disable-static --enable-gpl --enable-version3 --disable-openssl --enable-gnutls --enable-ladspa --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libdc1394 --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libjack --enable-libjxl --enable-librist --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopenh264-dlopen --enable-libopus --enable-libpulse --enable-librav1e --enable-librubberband --enable-libsvtav1 --enable-libsoxr --enable-libspeex --enable-libssh --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libxml2 --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lto --enable-lv2 --enable-libmfx --enable-vaapi --enable-vdpau --enable-version3 --enable-libfdk-aac-dlopen --enable-nonfree --enable-libvo-amrwbenc --enable-libx264 --enable-libx265 --enable-libxvid
  libavutil      58.  2.100 / 58.  2.100
  libavcodec     60.  3.100 / 60.  3.100
  libavformat    60.  3.100 / 60.  3.100
  libavdevice    60.  1.100 / 60.  1.100
  libavfilter     9.  3.100 /  9.  3.100
  libswscale      7.  1.100 /  7.  1.100
  libswresample   4. 10.100 /  4. 10.100
  libpostproc    57.  1.100 / 57.  1.100