Report consumption from run_event

`Event::consumes` says whether having run uses up what triggered it,
defaulting to no. `run_fn` already calls `should_run` per registration,
so it ors that across everything that ran and hands it back through
`run_event`. `CursorSenses` answers it with the sense it matched: a press
or a scroll is used up, hovering is not.

That drops `TypeEventManager::registered` and the second pass over a
widget's senses -- the match that decides consumption is now the same one
that decides whether the handler runs.

A cursor that is only resting still stops at the layer it is over, which
`run_event` cannot report because nothing need answer for it to be true.
It must not stop at a widget it has merely left, though, or ending a hover
above blocks the hover below: `leaving_a_widget_does_not_block_the_layer_below`
is that case, and it fails on `main` too.

core/src/event/mod.rs

@@ -13,6 +13,14 @@ pub trait Event: Sized + 'static + Clone {
     fn should_run<'a>(&self, data: &Self::Data<'a>) -> Option<Self::Data<'a>> {
         Some(data.clone())
     }
+
+    /// Whether having run on this data uses up whatever triggered it, so
+    /// nothing further should see it. `run_event` reports back the `or` of
+    /// this across everything that ran.
+    #[allow(unused_variables)]
+    fn consumes(&self, data: &Self::Data<'_>) -> bool {
+        false
+    }
 }
 
 pub trait EventLike {