libstdc++: Replace __int_limits with __numeric_traits_integer

libstdc++: Replace __int_limits with __numeric_traits_integer

I recently added std::__detail::__int_limits as a lightweight
alternative to std::numeric_limits, forgetting that the values it
provides (digits, min and max) are already provided by
__gnu_cxx::__numeric_traits.

This change adds __int_traits as an alias for __numeric_traits_integer.
This avoids instantiating __numeric_traits to decide whether to use
__numeric_traits_integer or __numeric_traits_floating. Then all uses of
__int_limits can be replaced with __int_traits, and __int_limits can be
removed.

libstdc++-v3/ChangeLog:

	* include/Makefile.am: Remove bits/int_limits.h.
	* include/Makefile.in: Regenerate.
	* include/bits/int_limits.h: Removed.
	* include/bits/parse_numbers.h (_Select_int_base): Replace
	__int_limits with __int_traits.
	* include/bits/range_access.h (_SSize::operator()): Likewise.
	* include/ext/numeric_traits.h (__numeric_traits_integer): Add
	static assertion.
	(__int_traits): New alias template.
	* include/std/bit (__rotl, __rotr, __countl_zero, __countl_one)
	(__countr_zero, __countr_one, __popcount, __bit_ceil)
	(__bit_floor, __bit_width) Replace __int_limits with
	__int_traits.
	* include/std/charconv (__to_chars_8, __from_chars_binary)
	(__from_chars_alpha_to_num, from_chars): Likewise.
	* include/std/memory_resource (polymorphic_allocator::allocate)
	(polymorphic_allocator::allocate_object): Likewise.
	* include/std/string_view (basic_string_view::_S_compare):
	Likewise.
	* include/std/utility (cmp_equal, cmp_less, in_range): Likewise.