libstdc++: Implement P2367 changes to avoid some list-initialization

libstdc++: Implement P2367 changes to avoid some list-initialization

This implements the wording changes of P2367R0 "Remove misuses of
list-initialization from Clause 24", modulo the parts that depend
on P1739R4 which we don't yet implement (due to LWG 3407).

libstdc++-v3/ChangeLog:

	* include/bits/ranges_util.h (subrange::subrange): Avoid
	list-initialization in delegating constructor.
	* include/std/ranges (single_view): Replace implicit guide
	with explicit deduction guide that decays its argument.
	(_Single::operator()): Avoid CTAD when constructing the
	single_view object.
	(_Iota::operator()): Avoid list-initialization.
	(__detail::__can_filter_view, _Filter::operator()): Likewise.
	(__detail::__can_transform_view, _Transform::operator()): Likewise.
	(take_view::begin): Likewise.
	(__detail::__can_take_view, _Take::operator()): Likewise.
	(__detail::__can_take_while_view, _TakeWhile::operator()): Likewise.
	(__detail::__can_drop_view, _Drop::operator()): Likewise.
	(__detail::__can_drop_while_view, _DropWhile::operator()): Likewise.
	(split_view::split_view): Use views::single when initializing
	_M_pattern.
	(__detail::__can_split_view, _Split::operator()): Avoid
	list-initialization.
	(_Counted::operator()): Likewise.
	* testsuite/std/ranges/p2367.cc: New test.