libstdc++: Reduce uses of std::numeric_limits

libstdc++: Reduce uses of std::numeric_limits

This avoids unnecessary instantiations of std::numeric_limits or
inclusion of <limits> when a more lightweight alternative would work.
Some uses can be replaced with __gnu_cxx::__int_traits and some can just
use size_t(-1) directly where SIZE_MAX is needed.

libstdc++-v3/ChangeLog:

	* include/bits/regex.h: Use __int_traits<int> instead of
	std::numeric_limits<int>.
	* include/bits/uniform_int_dist.h: Use __int_traits<T>::__max
	instead of std::numeric_limits<T>::max().
	* include/bits/hashtable_policy.h: Use size_t(-1) instead of
	std::numeric_limits<size_t>::max().
	* include/std/regex: Include <ext/numeric_traits.h>.
	* include/std/string_view: Use typedef for __int_traits<int>.
	* src/c++11/hashtable_c++0x.cc: Use size_t(-1) instead of
	std::numeric_limits<size_t>::max().
	* testsuite/std/ranges/iota/96042.cc: Include <limits>.
	* testsuite/std/ranges/iota/difference_type.cc: Likewise.
	* testsuite/std/ranges/subrange/96042.cc: Likewise.