shell: Set state_changed when we make a surface transient
shell: Set state_changed when we make a surface transient

If we don't mark the state as changed, we don't copy over next_state to
state and we fail to treat the surface as a transient.  In particular,
we give it a random intial position instead of mapping it at the given
parent relative position.

https://bugs.freedesktop.org/show_bug.cgi?id=72532

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