This makes picture_pool_Get() reentrant.

This reduces the size of picture_gc_sys_t. The callbacks are always the
same for all pictures in a given pool.

We can offload the picture deletion to Destroy() in all cases.

The item-change callback might be called very often, and thus an
own code path is better, with only necessary updates.

Additionally, this fixes multiple resume playback dialogs occuring
at once when starting playback in certain situations.

refs #11981

Also handles CustomAttributes

Was downloading regardless of consumer

Fixes most of glitches for non live streams, especially on
quality change.

CTTS value can be negative on version 0, and match the not found
return value used in GetPTSDelta.
ex: Sintel Smooth Streaming sample

The input stream id is completely unrelated to the input
sample buffer index - the sample allocated in AllocateInputSample
contains one single media buffer, at index 0.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

LeafDemuxer fixes (the experimental data-sequence driven
fragmented mp4 demux).

Some muxers are interleaving using single trun/fragments,
Moov()->Moov(A)->Moof(B)
instead of interlacing truns withing fragments.
Moov()->Moof(A,B)->Moof(A,B)
Example: BigBuckBunny ismv file

Another problem is that data isn't interleaved at all
at end of tracks, and there's a long trailing gap of
audio fragments only.
Moov()->Moov(A)->Moof(B)->Moof(B)->Moof(B)->Moof(B)