Avoid entering pip activity from affecting sysui appearance

Even if the pip activity is not focusable, its window could be
still added into mStatusBarAppearanceRegionList from
DisplayPolicy#applyPostLayoutPolicyLw before the animation is
finished to commit fullscreen to pinned mode.

So exclude the intermediate case to avoid status bar flickering
if the app requested APPEARANCE_LIGHT_STATUS_BARS.

Fix: 307214895
Test: atest RootWindowContainerTests#testSingleActivityTaskEnterPip
Change-Id: I3974f26fcc4d5c0ceb4a490eefc86169892ba1c4