Fix the interaction between _Pass_fn and invoke

[CaseyCarter]

_Pass_fn returns a copy of arguments no larger than void*, and a call-forwarding reference-wrapper-alike _Ref_fn for larger function objects. This became a problem when Ranges started throwing pointers-to-member at _Pass_fn with the expectation that they would eventually be invoked: pointers-to-member can be larger than void*, but _Ref_fn doesn't speak the invoke protocol.

There are two relatively obvious possible fixes:

1. Teach _Pass_fn to always return copies of pointers-to-member regardless of size
2. Teach _Ref_fn to obey the invoke protocol

(1) results in "large" pointers-to-member that can't be enregistered being copied and passed by hidden reference resulting in larger codesize than (2), but with no corresponding performance benefits. We therefore implement (2) by teaching _Ref_fn to call-forward through invoke when it wraps a pointer-to-member.

Fixes GH-1089.

[StephanTLavavej]

Quantum cats! ⚛️ 🐱 Thanks, I think your solution is better than what I would have come up with.

[BillyONeal]

It doesn't look like your title and message match the actual effects?

[CaseyCarter]

It doesn't look like your title and message match the actual effects?

Updated.

[CaseyCarter]

Thanks for fixing this bug that you should have noticed months ago!