Rename the [Ee]xts dir to ext (#38852)

**WARNING:** This PR will probably blow up all in-flight PRs

at some point in the early days of CmdPal, two of us created seperate
`Exts` and `exts` dirs. Depending on what the casing was on the branch
that you checked one of those out from, it'd get stuck like that on your
PC forever.

Windows didn't care, so we never noticed.

But GitHub does care, and now browsing the source on GitHub is basically
impossible.

Closes #38081

src/modules/cmdpal/ext/SamplePagesExtension/Pages/SampleMarkdownPage.cs

@@ -0,0 +1,172 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace SamplePagesExtension;
+
+internal sealed partial class SampleMarkdownPage : ContentPage
+{
+    public static readonly string SampleMarkdownText = @"
+# Markdown Guide
+
+Markdown is a lightweight markup language with plain text formatting syntax. It's often used to format readme files, for writing messages in online forums, and to create rich text using a simple, plain text editor.
+
+## Basic Markdown Formatting
+
+### Headings
+
+    # This is an <h1> tag
+    ## This is an <h2> tag
+    ### This is an <h3> tag
+    #### This is an <h4> tag
+    ##### This is an <h5> tag
+    ###### This is an <h6> tag
+
+### Emphasis
+
+    *This text will be italic*
+    _This will also be italic_
+
+    **This text will be bold**
+    __This will also be bold__
+
+    _You **can** combine them_
+
+Result:
+
+*This text will be italic*
+
+_This will also be italic_
+
+**This text will be bold**
+
+__This will also be bold__
+
+_You **can** combine them_
+
+### Lists
+
+**Inordered:**
+
+    * Milk
+    * Bread
+        * Wholegrain
+    * Butter
+
+Result:
+
+* Milk
+* Bread
+    * Wholegrain
+* Butter
+
+**Ordered:**
+
+    1. Tidy the kitchen
+    2. Prepare ingredients
+    3. Cook delicious things
+
+Result:
+
+1. Tidy the kitchen
+2. Prepare ingredients
+3. Cook delicious things
+
+### Images
+
+    ![Alt Text](url)
+
+Result:
+
+![painting](https://i.imgur.com/93XJSNh.png)
+
+### Links
+
+    [example](http://example.com)
+
+Result:
+
+[example](http://example.com)
+
+### Blockquotes
+
+    As Albert Einstein said:
+
+    > If we knew what it was we were doing,
+    > it would not be called research, would it?
+
+Result:
+
+As Albert Einstein said:
+
+> If we knew what it was we were doing,
+> it would not be called research, would it?
+
+### Horizontal Rules
+
+```markdown
+    ---
+```
+
+Result:
+
+---
+
+### Code Snippets
+
+    Indenting by 4 spaces will turn an entire paragraph into a code-block.
+
+Result:
+
+    .my-link {
+        text-decoration: underline;
+    }
+
+### Reference Lists & Titles
+
+    **The quick brown [fox][1], jumped over the lazy [dog][2].**
+
+    [1]: https://en.wikipedia.org/wiki/Fox ""Wikipedia: Fox""
+    [2]: https://en.wikipedia.org/wiki/Dog ""Wikipedia: Dog""
+
+Result:
+
+**The quick brown [fox][1], jumped over the lazy [dog][2].**
+
+[1]: https://en.wikipedia.org/wiki/Fox ""Wikipedia: Fox""
+[2]: https://en.wikipedia.org/wiki/Dog ""Wikipedia: Dog""
+
+### Escaping
+
+    \*literally\*
+
+Result:
+
+\*literally\*
+
+## Advanced Markdown
+
+Note: Some syntax which is not standard to native Markdown. They're extensions of the language.
+
+### Strike-throughs
+
+    ~~deleted words~~
+
+Result:
+
+~~deleted words~~
+
+
+";
+
+    public SampleMarkdownPage()
+    {
+        Icon = new IconInfo(string.Empty);
+        Name = "Sample Markdown Page";
+    }
+
+    public override IContent[] GetContent() => [new MarkdownContent(SampleMarkdownText)];
+}