defineConfig helper in newest ESLint 9.22

[devtobi]

eslint 9.22 introduced the helper function defineConfig (see https://eslint.org/blog/2025/03/flat-config-extends-define-config-global-ignores/#introducing-defineconfig()-for-eslint for more information).

As vuejs/eslint-config-typescript also provides its own helper function defineConfigWithVueTs, I wonder whether this is still necessary.
If so, the implementation of defineConfigWithVueTs should be refactored to use the eslint helper function. (e.g. flattening can be done by eslint helper function).

[haoqunjiang]

It's still necessary to transform the user-config inside the helper function.
The implementation is based on typescript-eslint's config helper, which has different semantics from the official one (typescript-eslint/typescript-eslint#10856). We'll need a breaking change to match it. Let's wait for typescript-eslint to catch it up first.