libstd++: Implement C++23 P2674R1 - A trait for implicit lifetime types

libstd++: Implement C++23 P2674R1 - A trait for implicit lifetime types

The following patch attempts to implement the library side of the
C++23 P2674R1 paper.  As mentioned in the paper, since CWG2605
the trait isn't really implementable purely on the library side.

The compiler side has been committed earlier, so this just uses
the new builtin trait on the library side.

2025-10-30  Jakub Jelinek  <jakub@redhat.com>

	* include/bits/version.def (is_implicit_lifetime): New.
	* include/bits/version.h: Regenerate.
	* include/std/type_traits (std::is_implicit_lifetime,
	std::is_implicit_lifetime_v): New trait.
	* src/c++23/std.cc.in (std::is_implicit_lifetime,
	std::is_implicit_lifetime_v): Export.
	* testsuite/20_util/is_implicit_lifetime/version.cc: New test.
	* testsuite/20_util/is_implicit_lifetime/value.cc: New test.