Support configuration file eslint.config.js

[jstritch]

ESLint is introducing a new flat configuration file structure. They make the statement We are transitioning to a new config system in ESLint v9.0.0. The config system shared on this page is currently the default but will be deprecated in v9.0.0. at https://eslint.org/docs/latest/use/configure/configuration-files. The new structure is described at https://eslint.org/docs/latest/use/configure/configuration-files-new.

I believe some changes are required for eslint-plugin-jsonc to work with the new format.

[ota-meshi]

Thank you for posting this issue.
I think we need to support the new config format after v9 is released. Please consider submitting a PR if you need it before then.