video_output/vout_subpictures.c: Fix filters appearing and disappearing when loaded for the first time.

The sys->filter_chain_update and sys->source_chain_update interacted with each other, because
the code was not carefull enough on when it is safe to overload 'sub-source' with the value of
'sub-filter'. The 'sub-filter' chain can also be a 'sub-source', but not the otherway around.

Refactor sfilter enabling and disabling. One glitch stays present:
A user needs to call libvlc_{logo,marq,adjust}_int{ p_mi, libvlc_{logo,marq,adjust}_Enable, twice initially. Once before setting options to get module to load and second after setting options. After this Enabling/Disabling works as expected.
NOTE: when changing an option one MUST call
libvlc_{logo,marq,adjust}_int{ p_mi, libvlc_{logo,marq,adjust}_Enable, again.

The patch removes the dependency on the deprecated function vlc_object_find_name()

Fix #11333

This shortcut is not supported on the mac, and will not work.

We already check that it is SHA1

Fix #11118

Fix f3334ccb

Fix warning:
initialization discards ‘const’ qualifier from pointer target type
     es_format_t *fmt = &es->fmt;

Introduced in 60044057

This reverts commit 33a939a7.

Fix #11387

Make mplayer timeline display nicer

Was meant as constant pointer and constant pointed data.

If p_chain->first is NULL, we should not take the address of first->filter.

Close #7241

We do not want the fallback on external packages here

Close #11434