Add a new property so that clocksync can setup "ts-offset" value
based on the first buffer and pipeline's running time when the
first arrived. Newly update "ts-offset" in this case would be
a value that allows outputting the first buffer without clock waiting.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/702>
The clocksync element is a generic element that can be
placed in a pipeline to synchronise passing buffers to the
clock at that point. This is similar to 'identity sync=true',
but because it isn't GstBaseTransform-based, it can process
GstBufferLists without breaking them into separate GstBuffers
In the hotdoc inspector for example, pads are instantiated with
g_object_new, other code paths to get/set properties already make
that check.
And update doc cache
* Making sure that `static inline` function are in the GIR (by first
defining them, and make sure to mark as skiped)
* Do not try to link to unexisting symbols
* Also generate GIR information about gst_tracers
