Coalesce layout traversal when resizing stacks

When resizing the docked stack, the other stacks are also resized,
leading to multiple layout traversals. Coalesce these by
introducing the concept of layout traversal coalscing.

In addition, don't cause layout refreshs for the stacks that are
currently not visible.

Bug: 25015474
Change-Id: I5692d00c044572a1bbb3ea218b0c31572585f5bd