input-capture: Ignore emulated scroll events

For each libinput scroll event we generate two clutter events
(continuous and discrete), one of them marked as emulated. libei
explicitly specifies that emulation of scrolling must be done in the
client (if desired) so drop the emulated one.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3637>

src/backends/meta-input-capture-session.c

@@ -1458,6 +1458,9 @@ meta_input_capture_session_process_event (MetaInputCaptureSession *session,
         if (!session->eis_pointer)
           return TRUE;
 
+        if (clutter_event_is_pointer_emulated (event))
+          break;
+
         finish_flags = clutter_event_get_scroll_finish_flags (event);
 
         if ((finish_flags & CLUTTER_SCROLL_FINISHED_HORIZONTAL))