This allows building sourcekitd and swift-refactor with `SWIFT_BUILD_SWIFT_SYNTAX=NO`. In these builds, the `relatedidents` and `find-syntactic-rename-ranges` requests will always return an error.
I will remove the `syntactic-rename` refactoring action in a follow-up commit. Clients should always ask for rename ranges and perform the rename by themselves instead of asking for a renamed file.
Make sure they handle the case when a property wrapper type's constructor is
called with the first argument coming from the var initializer, and the rest
from the custom attribute's argument.
