Partial implementation of C++20 of <ranges> header

Partial implementation of C++20 of <ranges> header

	* doc/doxygen/user.cfg.in: Add new header.
	* include/Makefile.am: Add new header.
	* include/Makefile.in: Regenerate.
	* include/precompiled/stdc++.h: Include new header.
	* include/std/ranges: New header.
	(ranges::sentinel_t, ranges::range_value_t, ranges::range_reference_t)
	(ranges::range_rvalue_reference_t, ranges::sized_range)
	(ranges::output_range, ranges::input_ranges, ranges::forward_range)
	(ranges::bidirectional_range, ranges::random_access_range)
	(ranges::contiguous_range, ranges::common::range): Define.
	* testsuite/24_iterators/headers/iterator/synopsis_c++20.cc: Check
	that disabled_sized_sentinel can be specialized.
	* testsuite/std/ranges/access/begin.cc: Include <ranges> instead of
	<iterator>.
	* testsuite/std/ranges/access/cbegin.cc: Likewise.
	* testsuite/std/ranges/access/cdata.cc: Likewise.
	* testsuite/std/ranges/access/cend.cc: Likewise.
	* testsuite/std/ranges/access/crbegin.cc: Likewise.
	* testsuite/std/ranges/access/crend.cc: Likewise.
	* testsuite/std/ranges/access/data.cc: Likewise.
	* testsuite/std/ranges/access/empty.cc: Likewise.
	* testsuite/std/ranges/access/end.cc: Likewise.
	* testsuite/std/ranges/access/end_neg.cc: Likewise.
	* testsuite/std/ranges/access/rbegin.cc: Likewise.
	* testsuite/std/ranges/access/rend.cc: Likewise.
	* testsuite/std/ranges/access/size.cc: Likewise.
	* testsuite/std/ranges/access/size_neg.cc: Likewise.
	* testsuite/std/ranges/headers/ranges/synopsis.cc: New test.
	* testsuite/std/ranges/range.cc: New test.
	* testsuite/std/ranges/refinements.cc: New test.
	* testsuite/std/ranges/sized.cc: New test.
	* testsuite/util/testsuite_iterators.h: Add aliases for range types.
	(output_iterator_wrapper::WritableObject::operator=): Add const
	qualifier so that output_iterator_wrapper satisfies writable.

From-SVN: r277697