tsdemux: switch SCTE 35 sections handling to a passthrough model

tsdemux: switch SCTE 35 sections handling to a passthrough model

Instead of modifying the splice times in the incoming sections
to running time and expecting eg mpegtsmux to convert those back
to its local PES time domain, which might be impossible when
those splice times are encrypted or the specification is extended,
transmit the needed information to the muxer as separate fields in
the event:

* A pts offset field can be used by the muxer in order to calculate
  a final pts_adjustment

* A rtime_map can be used by the muxer to determine the correct
  running times at which it should request keyframes

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/913>