The new tag is supported by all decoders that use the tag name table,
and the ID3v2 tag "TSOA" maps to it.

The Release Track Id uniquely identifies a recording on a release - that
is, even if a recording appears twice on a release (meaning that the
combination of recording and release id are not enough to figure out
which one it is), the release track id will allow differentiating the two.

The tag names are taken from
https://musicbrainz.org/doc/MusicBrainz_Picard/Tags/Mapping

Move code from the Vorbis and FLAC decoder plugins.

Enables using range-based "for".

Replaces g_strstrip().

This saves another 3% memory.

Fixes clang warning.

Fixes clang warning.

By accident, this declared a global variable instead of adding the
"packed" attribute.

Some tagging libraries (eg. TagLib) produce that variant.

Fixes broken CUE sheet song tags (regression by commmit 7e8d254b).