Our Moodle instance has over 2000 tags, and our administrator needed a way to quickly identify and fix some of the more common mistakes in tags names.

This patch adds a new optional parameter and form to manage.php as well as some logic to add an extra WHERE clause to the big tag-grabbing query.

I reused a lot of the form code from the "add new official tag" form, so the maintainer may want to clean that up (but it works fine as-is).

Attached is a diff against the MOODLE_19_STABLE version of /tag/manage.php