Each emitted declaration is annotated with the external_source_symbol with its own USR, to allow Clang's indexer to recognize this declaration as a Swift declaration with a specific USR
This allows you to import a method that returns the type of the context in which the method is declared when such
type is a generic parameter in another type. This means that it's now possible to bridge the initializer for
RawRepresentable enums.
This change extends the clang header printer to start emitting C++ classes for Swift struct types with the correct struct layout in them (size + alignment)
