add resolver to resolve absolute path in @import

[kscc25]

Use case:

.stylelintrc

    "csstools/value-no-unknown-custom-properties": [true, {
      "resolver": {
        "extensions": [".css"], 
        "paths": ["./src/assets/css"] 
        "moduleDirectories": ["node_modules"] 
      }
    }]

src/assets/css/styles.css

:root {
	--color1: red;
}

node_modules/awesome-package/button.css

:root {
	--button-radius: 2px;
}

Button.css

@import 'styles.css';
@import 'awesome-package/button.css';

.button {
    color: var(--color1);
    border-radius: var(--button-radius);
}

This is inspired by path resolver in https://github.com/postcss/postcss-import