feat: allow unsafely customise META_FIELDS

[yidingww]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Currently config array assumes name is the only meta field that should be treated as descriptive information when checking ignore and matching configs.

However, in certain scenarios, we should allow customization of the default META_FIELDS.

What changes did you make? (Give an overview)

Expose an UNSAFE_extraMetaFields, which will be combined with const META_FIELDS as the instance's this.metaFields, which will be used everywhere instead of const META_FIELDS.

Related Issues

N/A

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

N/A

[nzakas]

I'm sorry, I can't tell what use case you're trying to solve. In any case, this isn't the way we design APIs. If you have a use case in mind, please open an issue and describe it so we can discuss.

[comp615]

@nzakas this probably should have included a reference to the upstream patch where the author is trying to update config-inspector so that it more closely mirrors the REAL logic of ESlint: eslint/config-inspector#115