Account for tasks over splitscreen in RemoteTargetGluer

* Previously we defaulted to 2 handles, but we didn't take into
account the posibility of having assistant showing a translucent
task on top of 2 apps. Or other tasks such as Home controls.
* We can scale down the number of handles we have from
initialization (as done in assignTargetsForSplitscreen), but it's
a bit harder to scale up. This is a separate, larger problem in
that the handles are created and needed before onAnimationStart(),
so Launcher doesn't know exactly how many handles are needed to be
created for the recents animation, that's determined by the actual
onAnimationStart() call itself.
* There's a small known bug only in the split case where one of
the tasks shows up over the assistant task, but can live with that
to minimize changes. (peanutbutter@ to clarify?)

Demo: https://drive.google.com/file/d/1hqipfdym_rRXFsAW932es7UdxTx66Zu4/view?usp=drive_link&resourcekey=0-Ri_Kl0xCNN3E81StTh4vxw

As you can see, Assistant translucent overlay seems to work well,
but there are still some glitches with Home controls. Specifically,
there is a flicker, sometimes followed by a black screen, when
returning to the split tasks with Home controls open on top. The
flicker also happens with Assistant, but I haven't seen the black
screen for that case yet. In any case, the crash is avoided, so...
progress? (Also these flickers/black screen happen for Home controls
even without splitscreen).

Original change by peanutbutter@: ag/24830632

Test: Tested assistant result tasks with fullscreen and splitscreen,
and by itself. Seems to animate fine. Also tested with Home controls,
which animates fine and avoids the crash, but still has some issues
when re-opening the tasks as described above.
Flag: NA
Bug: 321328009

Change-Id: I0aa04a6a14cf723b34431855483662039c96e553