Correctly handle the INPUT_EVENT_ITEM_META and INPUT_EVENT_ITEM_META
instead of skipping the whole event processing code without even freeing
the callback_info_t data structure.

Closes: #8285

if the device was unplugged in the meantime, VLC will fallback on the default system device

(As for qtype, this is only used by the postproc video filter.)

All that code boiled down to selecting MPEG2 vs normal mode by the
postproc video filter. Now that libavcodec does not provide the data
anymore, the code had no more effects.

(This datum was only used by postproc anyway.)

macosx: re-write and simplify the apple event handlers for GetURL and OpenURL, make it respect 'macosx-autoplay' (close #6319)

There may be more I forgot about..

This is necessary to compile with libav.git HEAD or with contribs.
Streaming output still needs fixing.

Note that the input coded buffer is now only freed if the decoding
returns a decoded frame, or the buffer has been entirely consumed
(see *pp_block = NULL).

If the user explicitly asks for a filter, it's an error to not be able
to instatiate it.
This reverts commit 7b0761c4.