Add property "handle-segment-change" for user to allow pushing
custom segment event. For now, this property can work only for
time format GstSegment.
This property can be useful in case application controls timeline
of stream such as there is timestamp discontinuity but playback is
expected to be continuous. Multi-period scenario of MPEG-DASH is an
example of this use case.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/663>
To document it, we instantiate a subclass and inspect the properties
on the created object. Subclasses (in that case textrender) may
initialize those properties with a different default, we do not
want to expose that in the base class documentation.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/723>