Work on issue #77931346: The notification that should not be named appeared

Keep track of whether a foreground service has been shown in a
notification channel and, the first time one is, make sure the channel
is sufficiently important regardless of what the user or app last
set for it.

Bug: 77931346
Test: runtest systemui-notification
Change-Id: Idecad2dceb8cc918feec91ca1ee26edf3d3ab7de