Do not no-op fold/unfold Shell transitions

Adds TRANSIT_FLAG_DISPLAY_LEVEL_TRANSITION flag to
display update transitions to ensure that we don't
miss DisplayInfo updates if there is already a
collecting (but not started) display transition.

Fixes: 416768740
Flag: EXEMPT bugfix
Test: atest TransitionTests
Test: atest DisplayContentDeferredUpdateTests
Change-Id: Idcd853f1f73527626869984e0647e4513da6c55d