Fix heads up isolated notif icon race condition

If the HeadsUpAppearanceController reported that there is an isolated
notification icon *before* the heads up StatusBarIconView is inflated by
the NotifPipeline, then the isolated icon would fail to show.

This is fixed by combining both the renderList and isolatedIcon states,
as opposed to sampling the former when the latter changes.

Flag: ACONFIG com.android.systemui.notifications_icon_container_refactor DEVELOPMENT
Bug: 278765923
Test: atest SystemUITests
Change-Id: If4897d973bfa301fe65ba9428289b3b4e0bb8685