* include/std/ranges (__detail::__convertible_to_non_slicing): New
	helper concept.
	(__detail::__pair_like_convertible_to): Remove.
	(__detail::__pair_like_convertible_from): Add requirements for
	non-slicing conversions.
	(subrange): Constrain constructors with __convertible_to_non_slicing.
	Remove constructors from pair-like types. Add new deduction guide.
	* testsuite/std/ranges/subrange/lwg3282_neg.cc: New test.