ESLint v9 Flat Configs

[DonIsaac]

The community is asking for flat config support, so we need to add it. oxc-project/oxc#4720.

It looks like the most asked for approach is a migration step. Before we do this, there are several other config features we need to add.

I'd love to hear any feedback, comments, questions, or concerns.

Prerequisites

• feat(linter): support glob-based path overrides
• should we support extends as well?

Todo

• feat(cli): add flat config migration command

[Boshen]

Can we somehow hijack eslint and get the list of rules and configurations for us 🤔

I had this idea a long time ago: eslint/eslint#16557 (comment)

I want ESLint to give me a list of file paths and rule configurations, oxc will parse and lint the files in parallel and hand back all the necessary details for disable comments, code fixes and diagnostics reporting.

So eslint is kind of the "frontend" for configurations, and we (oxlint) take care of the rest.

(although we won't hand back data to eslint)