Add `ends(with:)`

[amomchilov]

This PR adds an end-counterpart to the built-in Sequence.starts(with:).

Checklist

• [x] I've added at least one test that validates that my change is working, if appropriate
• [x] I've followed the code style of the rest of the project
• [x] I've read the Contribution Guidelines
• [x] I've updated the documentation if necessary