xwayland: Reset scheduled frames after hiding tablet cursor

Hiding the tablet tool cursor results in it being hidden forever after.
This is due to the stale frame callback that will neither be disposed
or replaced. This can be reproduced in krita (X11) as the pointer
cursor is hidden while over the canvas.

Clearing the frame callback ensures the correct behavior in future
xwl_tablet_tool_set_cursor() calls (i.e. a new cursor surface being
displayed, and a new frame callback created), and is 1:1
with xwl_seat_set_cursor() for pointers.

Signed-off-by: Carlos Garnacho <carlosg@gnome.org>
3 jobs for xwayland-tablet-cursor-fix in 6 minutes and 29 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Image
passed #342656
debian-testing

00:00:24

 
  Build And Test
passed #342657
autotools-build-and-test

00:06:04

passed #342658
meson-build-and-test

00:02:08