The use of one-sided binary search introduced by a066217 changes behaviour on invalid, unsorted input (see llvm#75230 (comment)). Add input validation on `_LIBCPP_HARDENING_MODE_DEBUG` to help users.

* Change interface of `__is_sorted_until()` so that it accepts a sentinel that's of a different type than the beginning iterator, and to ensure it won't try to copy the comparison function object.
* Add one assertion for each input range confirming that they are sorted.
* Stop validating complexity of `set_intersection()` in debug mode, it's hopeless and also not meaningful: there are no complexity guarantees in debug mode, we're happy to trade performance for diagnosability.
* Fix bugs in `ranges_robust_against_differing_projections.pass`: we were using an input range as output for `std::ranges::partial_sort_copy()`, and using projections which return the opposite value means that algorithms requiring a sorted range can't use ranges sorted with ascending values if the comparator is `std::ranges::less`. Added `const` where appropriate to make sure we weren't using inputs as outputs in other places.