feat: normalize patterns to handle "./" prefix in files and ignores

[Pixel998]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Addresses issue where patterns starting with "./" were not correctly matched in files and ignores.

What changes did you make? (Give an overview)

Strip "./" from the start of strings in files and ignores so that they match as expected.

Related Issues

eslint/eslint#18757

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

[nzakas]

Thanks for taking a look at this. Overall, it looks good.

I think we have a question here: Is it safe to overwrite files in an existing object or should we be creating a new object? I think we may need to create a new object to be safe, but that would also increase the number of objects we create. And if we do that, perhaps we should only do so when files has at least one pattern starting with "./" and reuse every other config as-is?

@eslint/eslint-tsc what do you think?

[mdjermanovic]

I think we should create a new object when we need to modify its content. In this case, where at least one of its files / ignores patterns starts with "./" or "!./".

[mdjermanovic]

I changed the tag to feat as this enables patterns that are currently no-op.

[nzakas]

LGTM, thanks!

Would like @mdjermanovic to approve before merging.

[mdjermanovic]

LGTM, thanks!