Can we change some constexpr functions to consteval in C++20 and later?

[frederick-vs-ja]

Some constexpr functions in the standard library always return the same constant value. It seems that we can change some of them to consteval in C++20 and later modes.

It seems that the only difference happens on taking address. However, most standard library function are made non-addressable by WG21-P0551R3 in C++20, so ill-formedness on taking address seems OK.