In the case where the bufferlist is writable, send the
buffers immediately without adding to the refcount. This
allows writable buffers to maintain their writability, even
without implementing a chain_list function on the element.
Adds a test to verify this property, where a writable list
maintains refcount 1, but a readonly list increases it.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7894>
The event type for instant-rate-change events was poorly chosen,
leading to them being re-sent too late and even after EOS.
Add a mechanism in GstPad for the sticky event order to be
different to the value of the event type to fix that up.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3387>
