[llvm] [STLExtras] Introduce bind_{first, last}, [not_]equal_to (PR #175056)

[Yanzuo Liu via llvm-commits]

zwuis wrote:

What about introducing `bind_{front,back}` and putting them in "llvm/ADT/STLForwardCompat.h"? `std::bind_front` is introduced in C++20. `std::bind_back` is introduced in C++23.

https://github.com/llvm/llvm-project/pull/175056