SystemUI: make sure to expand all the way when flinging

If the panel height changes while an accessibility service pulls down
the status bar (or first time user pulls statusbar down WITH QS tiles
immediately after boot), the height may dynamically change and the
height animator will continue animating down to the original calculated
height.

While expanding the stautsbar down, add a layout listener which ensures
that the height animator's final target is properly set so it smoothly
animates all the way down.

Ref: CYNGNOS-1644

Change-Id: I08f03d9aa556622b5bd39ddcb65a74019dd599e4
Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>