Consider function templates as conformance candidates

From [Dooez](https://github.com/Dooez)
[Timofey Dovgal](https://github.com/Dooez)

If you decide on explicit signature requirement as part of conformance rule, then I would suggest allowing templates in case an exact signature match can be instantiated.
This can be checked and used via member function pointer conversion from template. gcc 16.1 ICEs, but gcc trunk works
Ret (T::* ptr)(Args...) = &template [:member_function_template_reflection:];
https://godbolt.org/z/qWMr75cbb

Start with the conformance rule's explicit signature requirement and the member function pointer conversion example in the issue, then compare the linked Godbolt behavior on GCC 16.1 and GCC trunk. Define whether an exact signature match can instantiate a member function template and document the resulting conformance behavior.

Written by the indexing model from the issue text.