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/EvilSamplesPage.cs

@@ -0,0 +1,132 @@
+// 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 System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace SamplePagesExtension;
+
+public partial class EvilSamplesPage : ListPage
+{
+    private readonly IListItem[] _commands = [
+       new ListItem(new EvilSampleListPage())
+       {
+           Title = "List Page without items",
+           Subtitle = "Throws exception on GetItems",
+       },
+       new ListItem(new ExplodeInFiveSeconds(false))
+       {
+           Title = "Page that will throw an exception after loading it",
+           Subtitle = "Throws exception on GetItems _after_ a ItemsChanged",
+       },
+       new ListItem(new ExplodeInFiveSeconds(true))
+       {
+           Title = "Page that keeps throwing exceptions",
+           Subtitle = "Will throw every 5 seconds once you open it",
+       },
+       new ListItem(new ExplodeOnPropChange())
+       {
+           Title = "Throw in the middle of a PropChanged",
+           Subtitle = "Will throw every 5 seconds once you open it",
+       },
+       new ListItem(new SelfImmolateCommand())
+       {
+           Title = "Terminate this extension",
+           Subtitle = "Will exit this extension (while it's loaded!)",
+       },
+        new ListItem(new NoOpCommand())
+        {
+           Title = "I have lots of nulls",
+           Subtitle = null,
+           MoreCommands = null,
+           Tags = null,
+           Details = new Details()
+           {
+               Title = null,
+               HeroImage = null,
+               Metadata = null,
+           },
+        },
+        new ListItem(new NoOpCommand())
+        {
+           Title = "I also have nulls",
+           Subtitle = null,
+           MoreCommands = null,
+           Details = new Details()
+           {
+               Title = null,
+               HeroImage = null,
+               Metadata = [new DetailsElement() { Key = "Oops all nulls", Data = new DetailsTags() { Tags = null } }],
+           },
+        },
+        new ListItem(new AnonymousCommand(action: () =>
+        {
+            ToastStatusMessage toast = new("I should appear immediately");
+            toast.Show();
+            Thread.Sleep(5000);
+        }) { Result = CommandResult.KeepOpen() })
+        {
+           Title = "I take just forever to return something",
+           Subtitle = "The toast should appear immediately.",
+           MoreCommands = null,
+           Details = new Details()
+           {
+               Body = "This is a test for GH#512. If it doesn't appear immediately, it's likely InvokeCommand is happening on the UI thread.",
+           },
+        }
+    ];
+
+    public EvilSamplesPage()
+    {
+        Name = "Evil Samples";
+        Icon = new IconInfo("👿"); // Info
+    }
+
+    public override IListItem[] GetItems() => _commands;
+}
+
+[System.Diagnostics.CodeAnalysis.SuppressMessage("StyleCop.CSharp.MaintainabilityRules", "SA1402:File may only contain a single type", Justification = "Sample code")]
+internal sealed partial class ExplodeOnPropChange : ListPage
+{
+    private bool _explode;
+
+    public override string Title
+    {
+        get => _explode ? Commands[9001].Title : base.Title;
+        set => base.Title = value;
+    }
+
+    private IListItem[] Commands => [
+      new ListItem(new NoOpCommand())
+           {
+               Title = "This page will explode in five seconds!",
+               Subtitle = "I'll change my Name, then explode",
+           },
+        ];
+
+    public ExplodeOnPropChange()
+    {
+        Icon = new IconInfo(string.Empty);
+        Name = "Open";
+    }
+
+    public override IListItem[] GetItems()
+    {
+        _ = Task.Run(() =>
+        {
+            Thread.Sleep(1000);
+            Title = "Ready? 3...";
+            Thread.Sleep(1000);
+            Title = "Ready? 2...";
+            Thread.Sleep(1000);
+            Title = "Ready? 1...";
+            Thread.Sleep(1000);
+            _explode = true;
+            Title = "boom";
+        });
+        return Commands;
+    }
+}