Fix T60194: Sequencer cut loses animation data for the right strip.
Fixing the first also fixes the second. First attempt was delaying
uniquename check at a later step of cut process, after everything had
been duplicated. While this fixed first issue, second one became even
more proeminent (it become active for all strips, and not only
video/audio movie strips in meta's).
So instead, passing along the list of (new) sequences, so that duplicated
seqs can be put there immediately, before checking for unique names,
henceforth ensuring even strips inside meta's get properly handled.
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