Whenever a new surface is created, we have to update the cursor focus,
even if there's no input event. So, we generate one motion event, and
reuse the code to update the proper cursor focus. We need to do this
for all surface roles - toplevels, popups, subsurfaces.
Fixes#1162
The user-visible issue is that newly-mapped xdg-shell* windows would
sometimes start with their top-left-corner, rather than their center, in
the center of the screen. This is because get_size() would
conservatively fall back on (width, height) == (0, 0) if both
set_window_geometry() had not been called, and it found
view->wlr_surface to be NULL.
But, view->wlr_surface is only set to non-NULL in view_map(). We call
get_size() before this. Fortunately, the wlr_surface in question is
accessible via view->xdg_shell{,_v6}->surface, so always fall back on
that. We can assert its presence instead of further falling back on
(width, height) == (0, 0).
Signed-off-by: Genki Sky <sky@genki.is>
