Mirroring the demux element and isomp4mux from gst-plugins-rs.
Tested against other Gst elements and MPV. Note that the later
apparently does not show correct results for flipped values.
Can be tested with:
```
gst-launch-1.0 \
videotestsrc num-buffers=90 ! \
taginject tags="image-orientation=rotate-90" ! \
capsfilter caps=video/x-raw,width=640,height=480,max-framerate=30/1 ! \
videoconvert ! \
queue ! \
openh264enc ! \
queue ! \
h264parse ! \
mp4mux ! \
filesink location=./test.mp4
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8371>
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