Fix: camelcase ignoreGlobals shouldn't apply to undef vars (refs #14857)

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

refs #14857, fixes #14591 (comment)

In ESLint v7.32.0, ignoreGlobals option in the camelcase rule doesn't apply to undefined variables.

/* eslint camelcase: ["error", { ignoreGlobals: true }] */

undefined_variable; // error

implicit_global = 1; // error

Online Demo (still v7.32.0)

The refactoring made in #14591 to support class fields accidentally changed this behavior.

What changes did you make? (Give an overview)

Fixed the camelcase rule to restore the v7.32.0 behavior in regard to the ignoreGlobals option and undefined variables, and added missing test cases.

Is there anything you'd like reviewers to focus on?

[snitin315]

Looks good.