feat(stylelint): create initial config

packages/xerox-stylelint-config/README.md

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+# @xerox/stylelint-config
+
+> Stylelint shareable configuration for Xerox projects.
+
+[![circleci status][circleci-badge]][circleci-link]
+[![npm package][npm-badge]][npm-link]
+[![license MIT][license-badge]][license-link]
+[![commit style angular][commit-style-badge]][commit-style-link]
+[![semantic-release][semantic-release-badge]][semantic-release-link]
+[![Dependabot Status][dependabot-badge]][dependabot-link]
+
+## Usage
+1. Install this config and stylelint as a `devDependency`:
+```bash
+yarn add stylelint @xerox/stylelint-config --dev
+# or
+npm install stylelint @xerox/stylelint-config --save-dev
+```
+2. Add the following to your `package.json`:
+```jsonc
+{
+  // ...
+  "stylelint": {
+    "extends": "@xerox/stylelint-config"
+  }
+  // ...
+}
+```
+
+---
+[LICENSE][license-link] | [CHANGELOG][changelog-link]
+
+[license-link]: ../../LICENSE
+[changelog-link]: ./CHANGELOG.md
+
+[circleci-badge]: https://flat.badgen.net/circleci/github/xeroxinteractive/config/master
+[circleci-link]: https://circleci.com/gh/xeroxinteractive/config/tree/master
+
+[npm-badge]: https://flat.badgen.net/npm/v/@xerox/stylelint-config?color=cyan
+[npm-link]: https://www.npmjs.com/package/@xerox/stylelint-config
+
+[license-badge]: https://flat.badgen.net/badge/license/MIT
+
+[commit-style-badge]: https://flat.badgen.net/badge/commit%20style/angular/purple
+[commit-style-link]: https://github.com/angular/angular.js/blob/master/DEVELOPERS.md#-git-commit-guidelines
+
+[semantic-release-badge]: https://flat.badgen.net/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80/semantic%20release/e10079
+[semantic-release-link]: https://github.com/semantic-release/semantic-release
+
+[dependabot-badge]: https://flat.badgen.net/dependabot/xeroxinteractive/config?icon=dependabot
+[dependabot-link]: https://dependabot.com

packages/xerox-stylelint-config/__tests__/configs.test.js

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+const standalone = require('stylelint/lib/standalone');
+const { join } = require('path');
+
+test.each(['index.js', 'sass.js'])('%s config valid', (filename) => {
+  return expect(
+    standalone({
+      code: 'a {}',
+      config: {
+        extends: `./${filename}`,
+      },
+      configBasedir: join(__dirname, '../'),
+    })
+  ).resolves.toBeTruthy();
+});

packages/xerox-stylelint-config/index.js

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+module.exports = {
+  extends: ['stylelint-config-recommended', 'stylelint-prettier/recommended'],
+  rules: {
+    'color-hex-length': 'long',
+    'max-empty-lines': 3,
+    'no-descending-specificity': null,
+  },
+};

packages/xerox-stylelint-config/package.json

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+{
+  "name": "@xerox/stylelint-config",
+  "version": "0.0.0",
+  "description": "Stylelint shareable configuration for Xerox projects.",
+  "keywords": [
+    "xerox",
+    "stylelint",
+    "stylelint-config"
+  ],
+  "main": "index.json",
+  "repository": "git@github.com:xeroxinteractive/config.git",
+  "homepage": "https://github.com/xeroxinteractive/config/blob/master/packages/xerox-stylelint-config",
+  "author": "Andrew Leedham <andrew.leedham@xerox.com>",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "peerDependencies": {
+    "stylelint": "*"
+  },
+  "devDependencies": {
+    "@xerox/prettier-config": "*",
+    "stylelint": "^12.0.1",
+    "stylelint-config-prettier": "^8.0.0",
+    "stylelint-config-recommended": "^3.0.0",
+    "stylelint-prettier": "^1.1.2",
+    "stylelint-scss": "^3.13.0"
+  }
+}

packages/xerox-stylelint-config/sass.js

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+module.exports = {
+  extends: './index.js',
+  plugins: ['stylelint-scss'],
+  rules: {
+    'at-rule-no-unknown': null,
+    'scss/at-rule-no-unknown': true,
+  },
+};