input: always use the demux for titles & seekpoints (fixes #8456)
input: add access & stream controls for current title and seekpoint
vdr: switch to ACCESS_GET_SEEKPOINT
vcd: switch to ACCESS_GET_(TITLE|SEEKPOINT)
vcdx: switch to ACCESS_GET_(TITLE|SEEKPOINT)
mpeg: implement title/seekpoint controls (refs #8455)

This is intended for VDR directories and Video CDs.
access: remove info.i_(update|title|seekpoint)
input: remove input_source_t.p_access
Remove unused variables
input: deprecate input_source_t.p_stream (refs #8455)