When `defined(__cpp_lib_concepts)`, `(back_|front_|)insert_iterator` are default constructible, and have `ptrdiff_t` as difference type.
Skip libc++ tests broken by this change.
* Reduce the amount of content included by <array>.
Resolves GH-462.
* Demote `back_inserter` and `iterator` to `<iterator>`.
* Demote `_Yarn` to `<xlocinfo>`.
* Demote `_Tidy_guard`, `_Tidy_deallocate_guard`, and `_Nothrow_compare` to `<xmemory>`.
* Promote `_Swap_ranges_unchecked` to `<xutility>`.
* Change `<array>` to include only `<xutility>`.
* Un-demote iterator.
* Workaround many RWC projects that expected std::min and std::max to come from <array>.
* Remove the `_STL_ASSERT` from `std::min` and `std::max`. We normally guard every `op<` with debug checks, but in this case we aren't using it to enforce something like a container invariant; the number of bad op<s we catch with it are likely microscopic.
* Delete `_Min_value` and `_Max_value` from `<utility>`.
* Move `min` and `max` to `<utility>` (in the exact position as the old `_Min_value` and `_Max_value`)
* Change all existing callers of `_Min_value` and `_Max_value` to call `(_STD min)` and `(_STD max)`, respectively.
* Homogenize vector algorithm guards.
Casey Carter
Billy O'Neal
Nikita Kniazev
Michael Schellenberger Costa
Stephan T. Lavavej