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.
This fixes custom attribute syntax highlighting on parameters and functions
(where function builders can be applied). They weren't being walked in
the function position previously and were walked out of source order in the
parameter position.
It also fixes rename of the property wrapper and function builder type
names that can appear in custom attributes, as well as rename of property
wrapper constructors, that can appear after the type names, e.g.
`@Wrapper(initialValue: 10)`. The index now also records these constructor
occurrences, along with implicit occurrences whenever a constructor is
called via default value assignment, e.g. `@Wrapper var foo = 10`, so that
finding calls/references to the constructor includes these locations.
Resolves rdar://problem/49036613
Resolves rdar://problem/50073641
