libstdc++: Implement P3138R5 views::cache_latest

libstdc++: Implement P3138R5 views::cache_latest

libstdc++-v3/ChangeLog:

	* include/bits/version.def (ranges_cache_latest): Define.
	* include/bits/version.h: Regenerate.
	* include/std/ranges (__detail::__non_propagating_cache::_M_reset):
	Export from base class _Optional_base.
	(cache_latest_view): Define for C++26.
	(cache_latest_view::_Iterator): Likewise.
	(cache_latest_view::_Sentinel): Likewise.
	(views::__detail::__can_cache_latest): Likewise.
	(views::_CacheLatest, views::cache_latest): Likewise.
	* testsuite/std/ranges/adaptors/cache_latest/1.cc: New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>