Allow notification reordering after user adjusts importance

After the user adjusts the priority of a notification, we need to
temporarily lift the VisualStabilityManager's ban on reordering
to allow the priority adjustment to take effect.

There's no clear signal as to when this reprieve should end --
eventually, we'll get a ranking update, but there's no way to tell
that it was the update that our change triggered. So instead we just
wait for 1000ms and then drop the adjustment ban again. If a few
extra reorders slip in during that time, so be it.

Test: atest, manual
Bug: 129772718
Change-Id: Iefb6917bb41935ed6bfc720b51738c66ffa83457