Audit Queries fall back to email when first/last names are nil (#23393)

* Audit Queries fall back to email when first/last names are nil

The audit page displays user information, and one column is "Name". Since we now allow nil first/last names, this
value can return as a single space character. Instead, I've changed `common/user-full-name` to fall back to returning
the user's email address if they have no first/last name values.

Additionally:
- since names can be nil, I've added sort by email to some of the queries for the audit page
- display names have been changed from "Name" to "Member" in several queries to better fit the fallback to email

* Add a test to check that audit pages have proper name fallback

* Try to get test passing in CI

* Make query work in MySQL by coalescing 'null' to empty string