Add support for extends in overrides config

[ota-meshi]

Which issue, if any, is this issue related to?

None, but related to #3128.

Is there anything in the PR that needs further explanation?

This PR adds support for extends in overrides config.

e.g.

{
  "overrides": [
    {
      "files": ["*.scss"],
      "extends": "stylelint-config-recommended-scss"
    }
  ]
}

This option allows users to use config by language.

[ybiquitous]

Looks good! Do we need to update the document about the overrides property?

E.g.

https://github.com/stylelint/stylelint/blob/bf2802506ff04d59c5e352c86de99552449859ac/docs/user-guide/configure.md#overrides

[ota-meshi]

I don't think we need to update the document.
If we don't merge this PR and don't support extends, I think we need to add it to document as an unsupported property.

[ybiquitous]

I see. LGTM 👍🏼