Add Config-at-end directive/support to Transitions

This is basically a way to tell the transition system (and WM)
that activities in a specific container should not have their
clients receive configuration changes until the END of the
transition animation.

Usage amounts to calling setConfigAtEnd(wtoken) on a WCT.

Bug: 202201326
Bug: 290992727
Test: atest TransitionTests#testConfigAtEnd
Change-Id: If4728eab6686a1d0e081af128606af150e0d7cc2