The code is simplified by using GQuarks for looking for caps features, and
removing inner loops.
Also, it's used the pad template caps to compare with the incoming caps because
is cheaper at the beginning of negotiation, where the pad template caps is used.
And, since the ANY caps where removed, there's no need to check for an initial
intersection.
Finally, the completion of caps features is done through a loop.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6698>
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