Refactor test/integration/tools/user.js

This testing "class" is a mess, it should at least be migrated to TypeScript so we know what operations are available of a testing user during a test.

Also, I plan to remove this file and make the "User" code available to another file to start using more and more TypeScript in the tests. Also, the editor will infer more data even in JS files if it imports JS resulting from a TypeScript file.

mentioned in commit ca4d7c46

mentioned in commit 1fa1ae6d

mentioned in commit 1edc424d