Replace `createConfig` with `defineConfig` from ESLint

As of March 2025, ESLint ships with a [`defineConfig`](https://eslint.org/blog/2025/03/flat-config-extends-define-config-global-ignores/) helper, which seems awfully similar to the `createConfig` helper that we are using. We should investigate whether we can make use of this and replace it if so.

Start by comparing the repository's createConfig helper with ESLint's defineConfig helper described in the linked ESLint blog post. Determine whether defineConfig can replace createConfig without changing the shareable configuration's behavior; the issue provides no file or test entry point.

Written by the indexing model from the issue text.