The ability to set actually set a type constraint on an output value is
currently guarded by the "output_type_constraints" experiment opt-in, so
any non-experiment-using configuration will always have ConstraintType
set to cty.DynamicPseudoType as shown in some of the unit tests updated
here.

Those who opt in to the experiment can specify a type constraint and
defaults using exactly the same syntax as for input variables, and
essentially get the same effect but in reverse: the type constraint and
defaults get applied at the boundary where the value is leaving the
module where it's declared, as opposed to when it's entering into a module
as for input variables.