For types imported from C++, the original clang::TypeDecl is saved in
the swift::Type and reused for conversions back to clang::QualType.
However, the conversion did not account for foreign reference types,
which should be mapped to a pointer to the C++ record type, rather than
the record type itself.
This bug first appeared as a function template instantiation failure
due to a sanity check performed by SwiftDeclConverter::foreignReferenceTypePassedByRef()
but may also affect other round-tripping type conversions.
The added test case demonstrates the template instantiation scenario,
where templates were being used to overcome Swift/C++ interop's current
lack of support for class inheritance.
rdar://134979343
If a foreign reference type has a custom retain function, emit a call to
it instead of emitting a call to objc_retainAutoreleasedReturnValue.
rdar://117353222
