avviddec, video.c, h265parse: Workaround for broken field-based interlaced encoders

avviddec, video.c, h265parse: Workaround for broken field-based interlaced encoders

Some encoders (e.g. Makito) have H265 field-based interlacing, but then
also specify an 1:2 pixel aspect ratio. That makes it kind-of work with
decoders that don't properly support field-based decoding, but makes us
end up with the wrong aspect ratio if we implement everything properly.
As a workaround, detect 1:2 pixel aspect ratio for field-based
interlacing, and check if making that 1:1 would make the new display
aspect ratio common. In that case, we override it with 1:1.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2577>