mxfdemux: Handle non-frame wrapping

mxfdemux: Handle non-frame wrapping

* If we have an index table for non-framed essence, we can handle it

* The demuxer has a state which indicates whether it will next fetch a KLV or
data contained *within* a KLV.

* The position on Essence Tracks always correspond to the next entry to fetch,
demuxer offset will be skipped accordingly whenever we switch between
partitions (in case of resyncs). A copy of the main clip/custom KLV for that
partition is kept to track the position within the essence of that partition.

* For clip/custom-wrapped raw audio, if the edit rate is too small (and would
cause plenty of tiny buffers to be outputted), specify a minimum number of edit
units per buffer.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2371>