Defer sub-activity layout while sub-activity cfg is deferred

When using config-at-end, sub-activity configuration changes
are blocked so that the client doesn't receive configs until
the end of a transition. However, layout was still running
at these levels which was wasteful and produced incorrect
results.

Fix this by also deferring layout calculations during the
same time that sub-activity configs are deferred and then
updating the layout when resumed.

Bug: 393159816
Test: move pip without resize and observe no flicker
Flag: EXEMPT bugfix
Change-Id: I7cafe7db6f5af71df688a24f9ab12a427b91f38d