Cros: Animate expand of notification in the QS Bubble

Before, popups always animated expand/collapse via MOVE.
For the Message Center in the QS Bubble, they snapped.

Introduce State::EXPAND_OR_COLLAPSE for UnifiedMessageListView. Only
enabled for the notifications refresh.

Only one notification may expand at a time. This is because all
animations in this view tree are animated via a SlideAnimator in
UnifiedMessageListView.

I decided against refactoring this so that each MessageViewContainer
could have its own SlideAnimator, allowing us to animate multiple at
once. Mainly because I found it a bit strange to tie those animators in
with other animations in UnifiedMessageListView.

Also, we are using SlideAnimator here instead of LayerAnimator because
we have to (in a future CL) animate the children of MessageViewContainer
separately.

All animation durations are per-spec.

Bug: 1272860
Change-Id: Icab7b7c2f214255059d81c107ae0a9b5927fb940
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3282986
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Andre Le <leandre@chromium.org>
Cr-Commit-Position: refs/heads/main@{#948199}