Release visual indicator on snap to stable bounds

When a desktop task is dragged to the status bar area but off-center so
that it doesn't invoke fullscreen (and it temporarily showed the visual
indicator during the drag), if the snapped/end bounds end up being the
before the drag bounds, then a WCT is skipped because there's no net
bounds change. However, the surface was still moved and should be
animated back, and the visual indicator shown needs to be released.
These two things weren't done before, so this change makes sure they are
done in this edge case.

Additionally, the animator used to snap back always showed a Toast when
the task was unresizable, but it's not necessary to show it if it's
snapping back because you went into unreachable areas, so it also
changes when the Toast is shown to only happen when attempting to
half-screen snaps and that fails because the task is unresizable.

Fix: 375120310
Fix: 352332857
Test: follow drag instructions in the commit description, and verify the
task surface snaps back to the stable bounds and dumping SF shown no
visual indicator surface
Flag: EXEMPT bugfix

Change-Id: Ie8daae317625631089357e29fc5d1f72a42ff1c3