Large video was being updated through scheduleLargeVideoUpdate even when
the large video container was hidden via CSS. This occurred in multiple
layout modes: tile view, stage filmstrip (with 2+ participants), and
etherpad editing. These updates caused expensive operations including
setting video streams, managing track listeners, updating avatars, and
running show/hide animations - all wasted CPU cycles since the container
wasn't visible.
The fix introduces a centralized shouldHideLargeVideo() function that checks
all cases where the large video container is hidden. This function is used in
selectParticipantInLargeVideo() to guard to not update the participant id.
A state listener monitors transitions from hidden to visible states and ensures
the large video participant id is properly updated when the container becomes
visible again and set to undefined when large video is hidden.
This improves performance by eliminating unnecessary video element manipulation
and handler execution across all layout modes where large video is not displayed.
