Add some functions used in eslint rules

[mathiasvr]

This adds some functions used by some built-in eslint rules through ast-utils, to make it easier to customize them.

[MichaelDeBoey]

Hi @mathiasvr!

Since this repo is unmaintained, you might want to re-open this PR in the @eslint-community fork https://github.com/eslint-community/eslint-utils

For more info about why we created this organization, you can read https://eslint.org/blog/2023/03/announcing-eslint-community-org