after delegatesFocus host.focus(): document=host, shadow=delegate
after delegatesFocus already focused host.focus(): document=host, shadow=delegate
after delegatesFocus tabindex host.focus(): document=tabindex-host, shadow=tabindex-delegate
after delegatesFocus inert host.focus(): document=before, shadow=null
after direct inert host delegate.focus(): document=before, shadow=null
after delegatesFocus empty host.focus(): before