Splitted the huge test/validators.js file into multiple subfiles, one per validator function. This makes it easier to read the test cases and maintain them as well. Did not change any test content, only moved existing cases to new files.

This will naturally cause conflicts with currently open PRs, but they should be easy to tackle, once this is mered.

Fixes: #1791

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)