Stopping to do it at the bin description level but properly
plugging them where they are needed and cleanly ghosting the pads
where it makes most sense.
This introduces support for GES to request pads on the most upstream
element in case no static pad can be ghosted.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/merge_requests/187>
APIs:
- ges_timeline_get_frame_time
- ges_timeline_get_frame_at
- ges_clip_asset_get_frame_time
- ges_clip_get_timeline_time_from_source_frame
Extracting ges_util_structure_get_clocktime to internal utilities adding
support for specifying timing values in frames with the special
f<frame-number> synthax.
