Previously, notifications disappearing under cursor (e.g., because closed
manually or open from another device) did not notify the manager
properly, as the leaveEventHook was not triggered. This could lead to
notifications staying around when not supposed to (see #28813).
This commit fixes that by explicitly notifying manager when the
notification widget disappears under the cursor.
Fixes#28813.
Nikolai Nechaev
7fcd84d08e