demux_mkv: support some raw PCM variants

This affects 64 bit floats and big endian integer PCM variants
(basically crap nobody uses). Possibly not all MS-muxed files work, but
I couldn't get or produce any samples.

Remove a bunch of format tags that are not needed anymore. Most of these
were used by demux_mov, which is long gone. Repurpose/abuse 'twos' as
mpv-internal tag for dealing with the PCM variants mentioned above.
demux_mf: uncrustify
demux_mf: use talloc
demux: kill libmng support

It's a dead format that was never used anywhere.