io/input: implement lazy event routing

This change defers event routing from the time the event is queued until
the time Events is called. This allows a future change to execute
commands immediately and to react to event order changes during a frame.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/input/pointer_test.go

@@ -1037,6 +1037,7 @@ func TestPassCursor(t *testing.T) {
 		Position: f32.Pt(10, 10),
 		Kind:     pointer.Move,
 	})
+	r.Frame(&ops)
 	if got := r.Cursor(); want != got {
 		t.Errorf("got cursor %v, want %v", got, want)
 	}