Fix words in test string by changing the string

Problem/Motivation

These are words in strings in tests, which also means it could be an array key. For these the change was to modify the string itself.

Steps to reproduce

Proposed resolution

1. barqux
2. bazbaz
3. cafr
4. corge
5. foobarbaz
6. foofoo
7. invalididentifier
8. lowline
9. quux
10. quxqux
11. qwerqwer
12. restplugin
13. stdclass
14. textformat
15. textwithsummary
16. theseparator
17. userid

Merge request link

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet