[interop] FRT doesn't allow retain/release with templated functions

[hyp]

I would like to import an FRT that uses a templated retain/release function. This is currently not allowed:

template <class P>
void retain(P* ptr) {
	ptr->retain();
}

template <class P>
void release(P* ptr) {
	ptr->release();
}

#define SWIFT_CXX_REF   \
    __attribute__((swift_attr("import_as_ref")))   \
    __attribute__((swift_attr("retain:retain")))   \
    __attribute__((swift_attr("release:release")))

class SWIFT_CXX_REF Ref { };

output:

error: cannot find retain function 'retain' for reference type 'Ref'

[ktoso]

rdar://102395866

[hyp]

Another example that we should support:

template <class P>
void retain(P* ptr) {
	ptr->retain();
}

template <class P>
void release(P* ptr) {
	ptr->release();
}

#define SWIFT_CXX_REF   \
    __attribute__((swift_attr("import_as_ref")))   \
    __attribute__((swift_attr("retain:retain")))   \
    __attribute__((swift_attr("release:release")))

template<class P>
class SWIFT_CXX_REF TemplateRef { };

using ConcreteRef = TemplateRef<int>;