[TypeChecker] PropertyWrappers: When setting projected value setter access account for `projectedValue` setter
Previously, the synthesis set the access of the setter of a newly
synthesized projected value property to match that of the parent
property setter, but `projectedValue` of the property wrapper could
be less accessible than that and the synthesis needs to account
for that. Otherwise, the interface file might get a setter printed
even though it's not part of the ABI.
Resolves: rdar://176978806