Deferring & deprioritizing participant search render

[mountiny]

Problem

In the Share Extension submit flow between ShareTabParticipantsSelector and SubmitDetailsPage, ParticipantSearchResults is expensive to render and was competing with navigation transitions. When going back from SubmitDetailsPage to ShareTabParticipantsSelector, the heavy search UI was mounting during the transition, causing jank.

Solution

We now treat that render as low priority. When navigating back, the navigation transition completes first, and ParticipantSearchResults mounts only once using Activity and useDeferVisibleUntilFocusTransitionEnd to wait for TransitionTracker before showing the search again. CustomViewWrapper was extracted from ScreenFreezeWrapper into DisplayContentsView so we can reuse the same native underlay during swipe-back without a blank flash.

PR

#96485

Issue Owner

Current Issue Owner: @jmgraa