Remove scroll-up effect from lockscreen swipe-up and unlock hint

by skipping notif stack height updates.

What caused the bug:
During swipe-up and unlock hint
PVC reduces stack height; since shadeBottom remains the same,
expansionFraction decreases, and so do notification heights.
Now that notifs are shorter, there's more room,
so a new notification starts to peek in above the shelf,
resulting in a scroll-up effect.

Note that we disable height updates for the above cases
instead of only allowing lockscreen notif stack height changes
for unfurl/to-shade/etc animations, since the latter approach
can miss edge cases that require stack height updates, resulting in regressions

Fixes: 217232659
Test: swipe up on lockscreen
	=> notif stack moves up, no height change
Test: tap lockscreen (not on any notif)
	=> ls bounces up and down, no height change for notif stack
Test: swipe away all notifs on lockscreen, no regressions
Test: open shade from top, use shade normally, no regressions

Change-Id: I80099b5892880f51aa0a90cbeeb2e1d981f52bc3