Proper icon validator

What does this MR do?

Sometimes the UX designers plan to rename/replace icons (see gitlab-svgs!117 (merged), gitlab-svgs!109 (merged) and gitlab-svgs#18 (closed)). While renaming is rather easy, we should catch wrong usages of icons during development/testing. The implementation works like this:

• HAML helper:
  • Production: Nothing happens
  • Development: Exception is thrown, you see a nice error screen
  • Testing (rspec): Exception is thrown, test fails
• Vue Component:
  • Production: Nothing happens
  • Development: Vue Prop Validator logs error to console.
  • Testing (karma): Vue Prop Validator logs error to console, karma fails because Validators are not allowed to fail during testing

The workflow then can look like this:

1. Change name in gitlab-svg
2. Forward gitlab-svg in CE/EE
3. Catch and fix all the errors with the tests
4. Fix the errors
5. ???
6. Profit!

Are there points in the code the reviewer needs to double check?

• Backend maintainer: Is the JSON just loaded in dev/test?

Does this MR meet the acceptance criteria?

• [n/a] Changelog entry added, if necessary
• [n/a] Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• [n/a] Conform by the database guides
• [n/a] If you have multiple commits, please combine them into a few logically organized commits by squashing them
• [n/a] Internationalization required/considered
• [n/a] End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/49236