The current valid pair nomination makes no effort to select pairs that
could have some similarities across different components and different
streams. This is normally not required by the RFC8445, but some well
known applications will misbehave when the libnice agent is in this
position to choose the nominated pairs (regular nomination mode, and
controlling mode) and if it makes an unexpected choice from the peer
point-of-view.

This patch improves the stopping criterion and the selection of the
preferred pair to nominate in that case.

When no other pair has been nominated yet (across all streams), the
previous stopping criterion still applies, and the best ranked pair of
the checklist is selected.

When a nominated pair exists from another component, we try to nominate
a pair of the same kind (same local and remote addresses and same
transport) if we have one, and possibly the best pair we have in the
checklist, and else we look for a nominated pair from another stream.