Issue Description:

As best described by @xwu in this comment:

Definitely, we should try to improve the situation, but I question if this is the optimal first bit of improvement. Frankly, as it's currently named, elementsEqual is confusing even for ordered collections; users are much more likely to be comparing two instances of the same type, and they should be reaching for == instead.

What I'm hinting at above is: this function-should it be useful-might be best off renamed to something like lexicographicallyMatches (a la lexicographicallyPrecedes). Then, to transition, a deprecation annotation can be affixed to an elementsEqual stub telling users to use == if possible and to avoid using elementsEqual on unordered collections. I'd also recommend coalescing lexicographicallyPrecedes(_:by: ) and elementsEqual(_:by: ) (the methods that take a custom predicate) into a single lexicographicallyCompares(_:by: ) as they're really not different.