cxxomfort: C++23 Backports

cxxomfort rel.20210622

Simple backports for C++ - http://ryan.gulix.cl/fossil.cgi/cxxomfort/

Backports from C++23.

A listing of some of the features backported:

From core: literal suffix for signed size_t.
From <functional>: invoke_r().
From <string> , <string_view>: contains().
From <string_view>: range constructor.
From <type_traits>: is_scoped_enum.

See also: C++20 Backports .