Update animation timing for split dismiss animation

* We weren't specifying an animation duration for the
dismiss placeholder animation, and it wasn't inheriting
from the animatorSet since that didn't have any duration
set on it.
* Now we explicitly set a duration (usually matching that of
the current launcher state config) to the timings line up
well

Test: Repro steps don't show bug. Also tested on large screen dismissing
contextual split from overview and home, seems fine
Fixes: 314860754

Change-Id: I701e4f88c1ddd92561da4fb76715a859f587c91e