This is a new opt-in flag for map settings/render context/layouts.
If set, then when applying clipping paths for selective masking,
we always use global ("entire map") paths, instead of calculating
local clipping paths per rendered feature. This results in
considerably more complex vector exports in all current Qt versions,
but gives us a way to force this IF/when a future Qt version adds
optimisations which make global masks desirable.
