Add some regexCondition() calls to the database API
As a follow-up to #47 (closed), the REGEXP is set in the system.admin.inc file. That is the only place in the core code that uses REGEXP in core at all, and it requires a case-insensitive search. The exact SQL differs between versions of MySQL (8.0.22 is an inflection point), and also varies by database platform.
This is the sort of thing that really belongs in the database layer, not in the main code.