Change error message for typo in helper's name

I've tried to make the error message more helpful, when helper name is misspelled. I created new type of error (MissingHelperModuleError) which is raised when expected constant is not loaded. I'd appreciate any feedback  about my solution.

Fixes #16468
@mnieborak don't :scissors: this

(I'm okay with the whitespace removal on 204/210)