When we generate a safe wrapper that only differs in the return type we
might introduce ambiguities as some callers might not have enough
information to disambiguate between the overloads. This PR makes sure
the newly generated declarations are marked as @_disfavoredOverload so
the compiler can keep calling the old functions without a source break
when the feature is turned on.
rdar://139074571
Support adding safe wrappers for APIs returning std::span depending on
the this object. This also fixes an issue for APIs with 0 parameters.
rdar://139074571
A previous PR already added support to the SwiftifyImport macro to
generate safe wrappers. This PR makes ClangImporter emit the macro to do
the transformation.
