compositor: Use pointer_cursor_surface_configure() in wl_pointer.set_cursor
compositor: Use pointer_cursor_surface_configure() in wl_pointer.set_cursor

This way we map the surface if it currently isn't mapped and avoid
duplicating some of the code already in pointer_cursor_surface_configure().
Without this, the cursor code relied on a wl_surface.attach() to show the
new pointer surface.  If we're not changing the cursor buffer, we don't
get that, but we still need to map the cursor.

giucam/weston,krezovic/weston,Fantu/compositor-spice,mchalupa/weston,jonnylamb/weston,eyolfson/weston,kwm81/weston,eyolfson/weston,udoprog/weston,sir-murray/weston,giucam/weston,udoprog/weston,krezovic/weston,sir-murray/weston,Gnurou/weston,Gnurou/weston,jonnylamb/weston,mchalupa/weston,Tarnyko/weston-xdg_surface_present,xorgy/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,xorgy/weston,kwm81/weston,Fantu/compositor-spice