Don't send unchecked a11y events from ExpandableNotificationRow

View#sendAccessibilityEventUnchecked(AccessibilityEvent event)
does not check whether accessibility is enabled or not, and
leaves this responsibility to the caller. Unfortunately this is the only
method that enables us to send a TYPE_WINDOW_CONTENT_CHANGED event with
defining its content change type.

This CL adds the required check for accessibility being enabled..

Bug: 380027122
Test: expand/collapse Notifications with TalkBack off
Flag: com.android.systemui.notification_row_accessibility_expanded

Change-Id: I82a43a3b60f2da493df3cff455d1329571943706