Fix __bitop_unsigned_integer and rename to __libcpp_is_unsigned_integer.
There are only five unsigned integer types, so we should just list them out.
Also provide `__libcpp_is_signed_integer`, even though the Standard doesn't
consume that trait anywhere yet.
Notice that `concept uniform_random_bit_generator` is specifically specified
to rely on `concept unsigned_integral` and *not* `__is_unsigned_integer`.
Instantiating `std::ranges::sample` with a type `U` satisfying
`uniform_random_bit_generator` where `unsigned_integral<U::result_type>`
and not `__is_unsigned_integer<U::result_type>` is simply IFNDR.
Orthogonally, fix an undefined behavior in std::countr_zero(__uint128_t).
Orthogonally, improve tests for the <bit> manipulation functions.
It was these new tests that detected the bug in countr_zero.
Differential Revision: https://reviews.llvm.org/D102328
Implements P1956: On the names of low-level bit manipulation functions.
Users may use older versions of libc++ or other standard libraries with the old names. In order to keep compatibility the old functions are kept, but marked as deprecated.
The patch also adds a new config macro `_LIBCPP_DEPRECATED_MSG`. Do you prefer a this is a separate patch?
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D90551
Arthur O'Dwyer