Fix dead surface/window left on screen

If the surface is explicitly hidden while we're changing resizing mode,
we need to discard the preserved surface immediately, otherwise it could
linger around on screen.

Do not mark mAnimatingExit in setTokenVisibilityLocked. This flag can only
be set after client relayouts to invisible. There we set mAnimatingExit and
mAnimating, so that when animation finishes the surface is marked to be
destroyed. If we marke it too early (and not mark mAnimating at the same
time), the surface may get stuck in exiting state.

bug: 28236574
Change-Id: I5cc916dfa698113e1d783a66547e1878469a9879