Restrict moveToSplit calls to freeform tasks.

The SplitScreenListener registered to desktop mode interferes with
the animation of moving tasks into split stage from recents. Restricting
it to freeform tasks restores the animation without impacting desktop
mode animations.

Bug: 338382550
Test: Manual, move to recents from one split pair, enter a second split pair, confirm animation plays. Confirm desktop functionality unaffected.
Change-Id: I0c17c6e14b2bcec18d5e3822f0437e11cbb5a73f