Pass events to the OSK in dialogs which grab events

With commit c29e0cf6e6 the grabHelper
already started using a similar mechanism to funnel events to the osk
while a ClutterGrab is in effect. ModalDialog, the unlockDialog and
lookingGlass don't make use of the grabHelper though, they use
Main.pushModal() themselves, so those need to funnel the events to the
OSK themselves.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2263>

js/ui/unlockDialog.js

@@ -625,6 +625,13 @@ var UnlockDialog = GObject.registerClass({
         return Clutter.EVENT_PROPAGATE;
     }
 
+    vfunc_captured_event(event) {
+        if (Main.keyboard.maybeHandleEvent(event))
+            return Clutter.EVENT_STOP;
+
+        return Clutter.EVENT_PROPAGATE;
+    }
+
     _createBackground(monitorIndex) {
         let monitor = Main.layoutManager.monitors[monitorIndex];
         let widget = new St.Widget({