Wait until updateItems is called to perform addStaticViews.

This is more consistent with pre-LayoutTransition approach, and should
behave more reliably on phones.

Flag: com.android.window.flags.enable_taskbar_recents_layout_transition
Bug: 343521765
Test: go/testedequals
Change-Id: Ib758b1e44c3b87d6d2ff71425ed40ff621261104