fix small layout bugs in app-settings-layout code example (#8622)

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### WHY are these changes introduced?

Found minor discrepancies in the app-settings-layout pattern example.

### WHAT is this pull request doing?

* Fixes inconsistent mobile padding for left hand column 
* Fixes description text not using <Text> component
* Adds missing mobile gap to Column component

<!-- ℹ️ Delete the following for small / trivial changes -->

### 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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  Give as much information as needed to experiment with the component
  in the playground.
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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/few-files-drop.md

@@ -0,0 +1,5 @@
+---
+'polaris.shopify.com': patch
+---
+
+Fix minor layout bugs in app-settings-layout pattern code example

polaris.shopify.com/content/patterns/app-settings-layout/variants/default.md

@@ -46,19 +46,19 @@ This pattern uses the [`AlphaStack`](/components/layout-and-structure/alpha-stac
   ]}
 >
   <AlphaStack gap="16" align="center">
-    <Columns columns={{xs: '1fr', md: '2fr 5fr'}}>
+    <Columns columns={{xs: '1fr', md: '2fr 5fr'}} gap="4">
       <Box
         as="section"
         paddingInlineStart={{xs: 4, sm: 0}}
-        paddingInlineEnd={{xs: 2, sm: 0}}
+        paddingInlineEnd={{xs: 4, sm: 0}}
       >
-        <AlphaStack align="start" gap="4">
+        <AlphaStack gap="4">
           <Text as="h3" variant="headingMd">
             InterJambs
           </Text>
-          <p>
+          <Text as="p" variant="bodyMd">
             Interjambs are the rounded protruding bits of your puzzlie piece
-          </p>
+          </Text>
         </AlphaStack>
       </Box>
       <AlphaCard roundedAbove="sm">
@@ -68,19 +68,19 @@ This pattern uses the [`AlphaStack`](/components/layout-and-structure/alpha-stac
         </AlphaStack>
       </AlphaCard>
     </Columns>
-    <Columns columns={{xs: '1fr', md: '2fr 5fr'}}>
+    <Columns columns={{xs: '1fr', md: '2fr 5fr'}} gap="4">
       <Box
         as="section"
-        paddingInlineStart={{xs: 2, sm: 0}}
-        paddingInlineEnd={{xs: 2, sm: 0}}
+        paddingInlineStart={{xs: 4, sm: 0}}
+        paddingInlineEnd={{xs: 4, sm: 0}}
       >
-        <AlphaStack align="start" gap="4">
+        <AlphaStack gap="4">
           <Text as="h3" variant="headingMd">
             Dimensions
           </Text>
-          <p>
+          <Text as="p" variant="bodyMd">
             Interjambs are the rounded protruding bits of your puzzlie piece
-          </p>
+          </Text>
         </AlphaStack>
       </Box>
       <AlphaCard roundedAbove="sm">