options: add some features to video filter parser

This is in preparation of making VOs and AOs use the parser which
originally was for video filters only.

The --vo and --ao options have several very annoying features, which are
added here:
- They can skip unknown video outputs (might be useful if a config file
  is supposed to work on several systems, where not all VOs/AOs are
  available everywhere)
- The trailing "," in "-vo a,b," was significant, and meant that if "a"
  and "b" don't work, try the normal autoprobe order as fallback
- There were deprecated VO names (like "gl3" and "gl"), which have to be
  handled with the option parser
- Separating VO/VF names and options is different
  ("-vf foo=opts" vs. "-vo foo:opts")
- vo_opengl.c provides opengl-hq as opengl + preset options

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