vlc_es: add defines for priority levels
mux: ogg: add skeleton metadata (fix #1412)

This patch adds Skeleton V4.0 metadata for multiplexed ogg streams.

Note this does not adds skeleton indexes to streams, as we need to
have a way to get sout position to reseek and rewrite that header from
keyframes.
mux: ogg: rewrite steam creation and ordering (fix #9731, fix #9732)

Ogg streams were invalid.
This patch ensures all streams have a way to end independently and
no other stream could start at arbitrary places. Also simplifies
a bit some code.

The ogg muxer suffers from an insufficient muxer cache value, and usually
starts streams before all streams have been declared.
The previous behaviour ( closing and restarting a new group of streams ) is kept
and fixed. But this is really not optimal.
We might need to consider increasing that cache for ogg.

It also handles correctly chained streams.
mux: ogg: add skeleton index

Adds the optional skeleton index for faster seeking.
Switches skeleton generation to Seekable input only case,
as we have no way to know values for fishead page before
the end of the encoding (total size, data start).