Check StatusBarState in isImportantForAccessibility.

We don't care about the transition specifically, but we just want to
make sure there's no "unlabelled" view on the lockscreen when there are
no notifications.

Bug: 293167744
Test: NotificationListViewModelTest + check with talkback if there's an
unlabelled view on the lockscreen
Flag: ACONFIG com.android.systemui.notifications_footer_view_refactor STAGING

Change-Id: I3f3ac8083dd054bdb7774fbf884e16bcc2bf126c