Tests: improve diffing for values of different types

[timmywil]

Summary

Differences are:

• use diffChars when both expected and actual are strings
• use diffWords for everything after that

Objects, arrays, and numbers are diffed as before.

Checklist

• [x] New tests have been added to show the fix or feature works
• [x] If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com