The Error enum synthesized declarations, e.g. the struct and its static accessors, should generally appear to be identical to the underlying Clang definitions. There are some specific use cases where the synthesized declarations are necessary though.
I've added an option for USR generation to override the Clang node and emit the USR of the synthesized Swift declaration. This is used by SwiftDocSupport so that the USRs of the synthesized declarations are emitted.
Fixes 79912
Based on feedback in PR https://github.com/swiftlang/swift/pull/69460, enabling indexing for synthesized decls because they are usable by users and make sense to appear in the indexstore.
Sets `synthesized` on some additional decls:
- derived `hashInto(...)`
- Objc properties and methods derived from Objc protocols
https://github.com/apple/swift/issues/67446