Implementation of three_way_comparable and three_way_comparable_with concepts from <compare> header.
Please note that I have temporarily removed <compare> header from <utility> due to cyclic dependency that prevents using <concepts> header in <compare> one.
I tried to quickly resolve those issues including applying suggestions from @cjdb and dive deeper by myself but the problem seems more complicated that we thought initially.
I am in progress to prepare the patch with resolving this cyclic dependency between headers but for now I decided to put all that I have to the review to unblock people that depend on that functionality. At first glance the patch with resolving cyclic dependency is not so small (unless I find the way to make it smaller and cleaner) so I don't want to mix everything to one review.