Leverage content/sandbox/index.md to create Sandbox nav link (#7427)

- update to use md convention to list sandbox route in navigation
- exclude /sandbox from catch all template

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### WHY are these changes introduced?

Fixes #0000 <!-- link to issue if one exists -->

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### WHAT is this pull request doing?

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### How to 🎩

🖥 [Local development
instructions](https://github.com/Shopify/polaris/blob/main/README.md#local-development)
🗒 [General tophatting
guidelines](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md)
📄 [Changelog
guidelines](https://github.com/Shopify/polaris/blob/main/.github/CONTRIBUTING.md#changelog)

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<details>
<summary>Copy-paste this code in
<code>playground/Playground.tsx</code>:</summary>

```jsx
import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
    </Page>
  );
}
```

</details>

### 🎩 checklist

- [ ] Tested on
[mobile](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md#cross-browser-testing)
- [ ] Tested on [multiple
browsers](https://help.shopify.com/en/manual/shopify-admin/supported-browsers)
- [ ] Tested for
[accessibility](https://github.com/Shopify/polaris/blob/main/documentation/Accessibility%20testing.md)
- [ ] Updated the component's `README.md` with documentation changes
- [ ] [Tophatted
documentation](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting%20documentation.md)
changes in the style guide

Author: gwyneplaine

.changeset/nine-icons-retire.md

@@ -0,0 +1,5 @@
+---
+'polaris.shopify.com': patch
+---
+
+Declare sandbox nav in a more idiomatic fashion

polaris.shopify.com/content/sandbox.md

@@ -0,0 +1,9 @@
+---
+title: Sandbox
+order: 10
+description: Cards are used to group similar concepts and tasks together to make Shopify easier for merchants to scan, read, and get things done.
+url: /sandbox?code=N4Igxg9gJgpiBcIA8BhAhgJygHQHYAJ8BnGSXKTATwDEIIAXGDAQTHoEsJciBeYAbWBlGuevHwByACLsiAW1lEJAXwC6yvIQAOGdnKq0GTVhy58hXEWMkBRAB5aIGevgBKMR85UbcAPk34qJhQAHQAEjBosBj4aGyc3HyC%2BMIwouISACoMaAA2%2BADKeTBK%2BGrK%2BBz0uTA82CBFNUT1-gSEgQAKEI4AbkwB7bHxfXwAZnkkPoOEcRw9aPROfAPTSABCAK70iwRQsmC5EEQbGDD4Wrlo7H4r0-gAauwwAO6Fxc1td0gA9JvbXK07lNplwUIcSHwABQASnwPF8%2BGAymBhEBqxMCQAMrIXOxGHJeAILKI0tYJABxDBHIhvJoqAA0iNS6UkADkYC5GiUVOp8N80YQfl1ekw0T90FhwpFomKJaECqRTDdPoFMjA7PQUJYrrhRbd8ABNCAbFJoAgbEjEd74U6eeg0xbEGBna6jJz6JWxABGxpclGNMTAFsWciYREAmAT6pzRGletAkKD4LgpXSMXRoYgbMAAC1iNKI1ogfRiHFDjK9lBS2bNutyjKc%2BAr%2BqI9DQo1GIRWPzVGq1oh1era4uCIQV8QBASCkrHnqqNTqIGyrfyXJpa1OaAA1lAIM9cC0u%2B4iAGwDBsS39adjydT6y0KHzERrgBzDaXDAZAs1CSMi4nPKfu83j6niMAEkk%2BqEMAkHtF%2BJQZAA8lgYY-jBMxyMaLISAAqgUUgACQAAwhIRhGoSqdwnLkGS2k49rfNGKH0jByjMRR7TQexgxwUQGTuPQJzcORdyDPemFkgAtLhBEAEwAKzEaRwkiYQVE0R4dFEN8pwCRgQlsSprH6uol5pNEACS%2BJQqBciwvCiIwWQLaIjxjJiRsoiMlRFQ8PgNkANwwTpgn4JCaGBEeJ5njiISWWB4WqRguR8N5CVDKeRBPl67C5HilCYmgXowMlwAAAaPC8tIlPgboxPhwA8copUoip%2BACq1SAFK2YCbu1rWBF1cSbrF%2BI1TluS%2BA17zKD8g09SNYF9R1c3DXFciTe5ogzd8K0LetaWzd1vXhT8kU3tFLZ7UthDQoF7HIvq-KTt8cqjoqCSyiOM4JJUeLzvUUiRMMCwwImtHOM0ICZl6UAbKD7VIOe9BLYjMVrb4HRoP6WxED8SNXfqqOXejS55FVa6Vig1a4LWeNo-iCPfEjYovV970TkOr3fcmc61PUrJGAeKpID2mratcg53Jk2ZnDxNoaRDsSnLE8w5YVNRJrguSVuwoz4NjMQtk4Lo0jzMuFNm3S65Q%2BoXGaSYxNm7DPjLGCdsL3yi32rYSxgLNc%2BzyrDlgvggPSID0DLoZEAg-AgIcYDFPAaQgKo4fPOwUCRzH8D8OoQA
+status:
+  value: Alpha
+  message: This component is in development. There could be breaking changes made to it in a non-major release of Polaris. Please use with caution.
+---

polaris.shopify.com/pages/[...slug].tsx

@@ -45,7 +45,8 @@ export const getStaticProps: GetStaticProps<Props, {slug: string[]}> = async ({
     throw new Error('Expected params.slug to be defined (as string[])');
 
   const slugPath = `${contentDir}/${params.slug.join('/')}`;
-  const pathIsDirectory = fs.existsSync(slugPath) && fs.lstatSync(slugPath).isDirectory();
+  const pathIsDirectory =
+    fs.existsSync(slugPath) && fs.lstatSync(slugPath).isDirectory();
   const mdRelativePath = pathIsDirectory
     ? `${contentDir}/${params.slug.join('/')}/index.md`
     : `${contentDir}/${params.slug.join('/')}.md`;
@@ -77,6 +78,7 @@ const catchAllTemplateExcludeList = [
   '/content',
   '/patterns',
   '/tokens',
+  '/sandbox',
 ];
 
 function fileShouldNotBeRenderedWithCatchAllTemplate(path: string): boolean {

polaris.shopify.com/src/components/Frame/Frame.tsx

@@ -6,7 +6,7 @@ import {motion, AnimatePresence} from 'framer-motion';
 
 import GlobalSearch from '../GlobalSearch';
 import navJSON from '../../../.cache/nav.json';
-import {NavJSON, NavItem, Breakpoints, StatusName} from '../../types';
+import {NavJSON, NavItem, Breakpoints} from '../../types';
 
 import styles from './Frame.module.scss';
 import {className} from '../../utils/various';
@@ -146,27 +146,6 @@ function Frame({darkMode, children}: Props) {
               handleLinkClick={() => setNavIsVisible(false)}
               handleShiftTabOnFirstLink={handleShiftTabPress}
             />
-            <li key="sandbox-route">
-              <span className={className(styles.NavItem)}>
-                <Link
-                  href={
-                    '/sandbox?code=N4Igxg9gJgpiBcIA8BhAhgJygHQHYAJ8BnGSXKTATwDEIIAXGDAQTHoEsJciBeYAbWBlGuevHwByACLsiAW1lEJAXwC6yvIQAOGdnKq0GTVhy58hXEWMkBRAB5aIGevgBKMR85UbcAPk34qJhQAHQAEjBosBj4aGyc3HyC%2BMIwouISACoMaAA2%2BADKeTBK%2BGrK%2BBz0uTA82CBFNUT1-gSEgQAKEI4AbkwB7bHxfXwAZnkkPoOEcRw9aPROfAPTSABCAK70iwRQsmC5EEQbGDD4Wrlo7H4r0-gAauwwAO6Fxc1td0gA9JvbXK07lNplwUIcSHwABQASnwPF8%2BGAymBhEBqxMCQAMrIXOxGHJeAILKI0tYJABxDBHIhvJoqAA0iNS6UkADkYC5GiUVOp8N80YQfl1ekw0T90FhwpFomKJaECqRTDdPoFMjA7PQUJYrrhRbd8ABNCAbFJoAgbEjEd74U6eeg0xbEGBna6jJz6JWxABGxpclGNMTAFsWciYREAmAT6pzRGletAkKD4LgpXSMXRoYgbMAAC1iNKI1ogfRiHFDjK9lBS2bNutyjKc%2BAr%2BqI9DQo1GIRWPzVGq1oh1era4uCIQV8QBASCkrHnqqNTqIGyrfyXJpa1OaAA1lAIM9cC0u%2B4iAGwDBsS39adjydT6y0KHzERrgBzDaXDAZAs1CSMi4nPKfu83j6niMAEkk%2BqEMAkHtF%2BJQZAA8lgYY-jBMxyMaLISAAqgUUgACQAAwhIRhGoSqdwnLkGS2k49rfNGKH0jByjMRR7TQexgxwUQGTuPQJzcORdyDPemFkgAtLhBEAEwAKzEaRwkiYQVE0R4dFEN8pwCRgQlsSprH6uol5pNEACS%2BJQqBciwvCiIwWQLaIjxjJiRsoiMlRFQ8PgNkANwwTpgn4JCaGBEeJ5njiISWWB4WqRguR8N5CVDKeRBPl67C5HilCYmgXowMlwAAAaPC8tIlPgboxPhwA8copUoip%2BACq1SAFK2YCbu1rWBF1cSbrF%2BI1TluS%2BA17zKD8g09SNYF9R1c3DXFciTe5ogzd8K0LetaWzd1vXhT8kU3tFLZ7UthDQoF7HIvq-KTt8cqjoqCSyiOM4JJUeLzvUUiRMMCwwImtHOM0ICZl6UAbKD7VIOe9BLYjMVrb4HRoP6WxED8SNXfqqOXejS55FVa6Vig1a4LWeNo-iCPfEjYovV970TkOr3fcmc61PUrJGAeKpID2mratcg53Jk2ZnDxNoaRDsSnLE8w5YVNRJrguSVuwoz4NjMQtk4Lo0jzMuFNm3S65Q%2BoXGaSYxNm7DPjLGCdsL3yi32rYSxgLNc%2BzyrDlgvggPSID0DLoZEAg-AgIcYDFPAaQgKo4fPOwUCRzH8D8OoQA'
-                  }
-                  onClick={() => setNavIsVisible(false)}
-                  passHref
-                >
-                  <a aria-current={'false'}>
-                    Sandbox
-                    <StatusBadge
-                      status={{
-                        message: 'Alpha',
-                        value: StatusName.Alpha,
-                      }}
-                    ></StatusBadge>
-                  </a>
-                </Link>
-              </span>
-            </li>
           </ul>
           <button
             ref={closeButtonRef}