Two issues were present in code that was resetting CRF quality level
to "do not use CRF, use bitrate settings" mode:
- It did not include AV1 codec, so whenever you switched to AV1 the CRF
was changing to constant bitrate.
- It wrongly included DNxHD codec. That seemed like it was trying to
fix#100079 in 06a01168f6, but it was doing exactly the opposite
of what a fix should have been? I don't understand it :/ In any case,
now with DNxHD removed the CRF properly switches to constant bitrate
when changing codec to DNxHD.
Factored the actual logic into BKE_ffmpeg_codec_supports_crf function.
