wayland: Use pop shell type for all transient style of surfaces

It's easy to test this functionality by opening a sub-window (e.g. right click
on the Web content), and without closing it go outside the Chromium window and
hover the mouse cursor over another Wayland application. Now, none interaction
using the mouse pointer should happen on those applications unless you click
again. IWO input grabbing across applications now are alright because Wayland
does it implicitly.