Speeds up vlc_list_find(), as we avoid looking up the 200+ plugins for
each vlc_list_find(). Also avoids accidentally stealing objects across
LibVLC instances. IMHO, the object tree should be per-instance, and the
root object should not exist, but that's too big a change yet.

(main remaining offenders: vlc_interface.h and vlc_network.h)

This reverts commit 62b9f5b0.

libvlccore: Rename iso_lang.h to vlc_iso_lang.h because we use VLC_EXPORT there, and plugins may use it.

Remove workarounds for broken (probably very old) FFmpeg .pc files
Errors out if nor swscale headers, nor img_resample() in libavcodec are
present

If stats are too heavy weight to use w/o debug, we should either fix
them or remove them completely anyway

Fix the rawvideo codec when visible_pitch != pitch. (And simplify code) This should fix partial screen captures using non multiple of 16 values.

Add some missing symbols in a blind attempt to fix the buildbots. Feel free to revert if this is wrong.