with Opus, use the specific tags for R128 gain data

[calestyo]

Hey.

Opus has it's own special tags for R128 gain data:

• R128_TRACK_GAIN
• R128_ALBUM_GAIN

See https://datatracker.ietf.org/doc/html/rfc7845#section-5.2.1 .

Would be nice if one could select whether only these (default), only replaygain or both types of tags would be written.

Default to only write Opus' type because of the RFC which says:

To avoid confusion with multiple normalization schemes, an Opus comment header SHOULD NOT contain any of the REPLAYGAIN_TRACK_GAIN, REPLAYGAIN_TRACK_PEAK, REPLAYGAIN_ALBUM_GAIN, or REPLAYGAIN_ALBUM_PEAK tags, unless they are only to be used in some context where there is guaranteed to be no such confusion.

Thanks.