libstdc++: Introduce new headers for C++20 ranges components

libstdc++: Introduce new headers for C++20 ranges components

This introduces two new headers:

<bits/ranges_base.h> defines the minimal components needed
for using C++20 ranges (customization point objects such as
std::ranges::begin, concepts such as std::ranges::range, etc.)

<bits/ranges_util.h> includes <bits/ranges_base.h> and additionally
defines subrange, which is needed by <bits/ranges_algo.h>.

Most of the content of <bits/ranges_base.h> was previously defined in
<bits/range_access.h>, but a few pieces were only defined in <ranges>.
This meant the entire <ranges> header was needed in <algorithm> and
<memory>, even though they don't use all the range adaptors.

By moving the ranges components out of <bits/range_access.h> that file
is left defining just the contents of [iterator.range] i.e. std::begin,
std::end, std::size etc. and not C++20 ranges components.

For consistency with other C++20 ranges headers, <bits/range_cmp.h> is
renamed to <bits/ranges_cmp.h>.

libstdc++-v3/ChangeLog:

	* include/Makefile.am: Add new headers and adjust for renamed
	header.
	* include/Makefile.in: Regenerate.
	* include/bits/iterator_concepts.h: Adjust for renamed header.
	* include/bits/range_access.h (ranges::*): Move to new
	<bits/ranges_base.h> header.
	* include/bits/ranges_algobase.h: Include new <bits/ranges_base.h>
	header instead of <ranges>.
	* include/bits/ranges_algo.h: Include new <bits/ranges_util.h>
	header.
	* include/bits/range_cmp.h: Moved to...
	* include/bits/ranges_cmp.h: ...here.
	* include/bits/ranges_base.h: New header.
	* include/bits/ranges_util.h: New header.
	* include/experimental/string_view: Include new
	<bits/ranges_base.h> header.
	* include/std/functional: Adjust for renamed header.
	* include/std/ranges (ranges::view_base, ranges::enable_view)
	(ranges::dangling, ranges::borrowed_iterator_t): Move to new
	<bits/ranges_base.h> header.
	(ranges::view_interface, ranges::subrange)
	(ranges::borrowed_subrange_t): Move to new <bits/ranges_util.h>
	header.
	* include/std/span: Include new <bits/ranges_base.h> header.
	* include/std/string_view: Likewise.
	* testsuite/24_iterators/back_insert_iterator/pr93884.cc: Add
	missing <ranges> header.
	* testsuite/24_iterators/front_insert_iterator/pr93884.cc:
	Likewise.