List postcss-values-parser as an import alias in the ESLint config

This is similar to how other packages are handled, note e.g. the `fluent` ones.

eslint.config.mjs

@@ -117,6 +117,7 @@ export default [
             "web",
             "fluent-bundle",
             "fluent-dom",
+            "postcss-values-parser",
             // See https://github.com/firebase/firebase-admin-node/discussions/1359.
             "eslint-plugin-perfectionist",
           ],

external/stylelint/no-unused-custom-properties.mjs

@@ -13,8 +13,6 @@
  * limitations under the License.
  */
 
-// TODO: Remove the exception below once someone figures out how to fix it.
-// eslint-disable-next-line import/no-unresolved
 import { parse, registerWalkers, Root } from "postcss-values-parser";
 import { isString } from "stylelint/lib/utils/validateTypes.mjs";
 import stylelint from "stylelint";