CmdPal: Plain text viewer and image viewer IContent (#43964)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

This PR introduces new types of IContent:  
- Plain text content – simple and straightforward, with options to
switch between UI and monospace fonts and toggle word wrap.
- It's super safe to display any random text content without having to
worry about escaping the pesky markdown.
- Image viewer content – a more polished way to display images:  
- When placed in the ContentPage, the component automatically resizes to
fit the viewport, ensuring the entire image is visible at once.
- Images can be opened in a built-in mini-viewer that lets you view,
pan, and zoom without leaving the Command Palette. (Doing this directly
on the page proved to be a UX and development headache.) Fully
keyboard-controllable, so there’s no need to take your hands off the
keys.

## Pictures? Pictures!

Plain text content:

<img width="960" height="604" alt="image"
src="https://github.com/user-attachments/assets/a4ec36f3-2f7f-4a2a-a646-53056c512023"
/>

Image viewer content:

<img width="939" height="605" alt="image"
src="https://github.com/user-attachments/assets/c87f5726-8cd0-4015-b2d9-f1457fa1ec96"
/>



https://github.com/user-attachments/assets/915cd9d2-e4e3-4baf-8df6-6a328a3592ba


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## PR Checklist

- [x] Closes: #41038
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/Helpers/Icons/IconLoaderService.cs

@@ -16,6 +16,8 @@ namespace Microsoft.CmdPal.UI.Helpers;
 
 internal sealed partial class IconLoaderService : IIconLoaderService
 {
+    public static readonly Size NoResize = Size.Empty;
+
     private const DispatcherQueuePriority LoadingPriorityOnDispatcher = DispatcherQueuePriority.Low;
     private const int DefaultIconSize = 256;
     private const int MaxWorkerCount = 4;
@@ -214,11 +216,6 @@ internal sealed partial class IconLoaderService : IIconLoaderService
     private static IconSource? GetStringIconSource(string iconString, string? fontFamily, Size size)
     {
         var iconSize = (int)Math.Max(size.Width, size.Height);
-        if (iconSize == 0)
-        {
-            iconSize = DefaultIconSize;
-        }
-
         return IconPathConverter.IconSourceMUX(iconString, fontFamily, iconSize);
     }
 }

src/modules/cmdpal/Microsoft.CmdPal.UI/Helpers/Icons/IconProvider.cs

@@ -11,7 +11,7 @@ namespace Microsoft.CmdPal.UI.Helpers;
 /// <summary>
 /// Common async event handler provides the cache lookup function for the <see cref="IconBox.SourceRequested"/> deferred event.
 /// </summary>
-public static partial class IconCacheProvider
+public static partial class IconProvider
 {
     /*
       Memory Usage Considerations (raw estimates):
@@ -29,6 +29,7 @@ public static partial class IconCacheProvider
     private static IIconSourceProvider _provider32 = null!;
     private static IIconSourceProvider _provider64 = null!;
     private static IIconSourceProvider _provider256 = null!;
+    private static IIconSourceProvider _providerUnbound = null!;
 
     public static void Initialize(IServiceProvider serviceProvider)
     {
@@ -37,6 +38,7 @@ public static partial class IconCacheProvider
         _provider32 = serviceProvider.GetRequiredKeyedService<IIconSourceProvider>(WellKnownIconSize.Size32);
         _provider64 = serviceProvider.GetRequiredKeyedService<IIconSourceProvider>(WellKnownIconSize.Size64);
         _provider256 = serviceProvider.GetRequiredKeyedService<IIconSourceProvider>(WellKnownIconSize.Size256);
+        _providerUnbound = serviceProvider.GetRequiredKeyedService<IIconSourceProvider>(WellKnownIconSize.Unbound);
     }
 
     private static async void SourceRequestedCore(IIconSourceProvider service, SourceRequestedEventArgs args)
@@ -80,5 +82,8 @@ public static partial class IconCacheProvider
 
     public static void SourceRequested256(IconBox sender, SourceRequestedEventArgs args)
         => SourceRequestedCore(_provider256, args);
+
+    public static void SourceRequestedOriginal(IconBox sender, SourceRequestedEventArgs args)
+        => SourceRequestedCore(_providerUnbound, args);
 #pragma warning restore IDE0060 // Remove unused parameter
 }

src/modules/cmdpal/Microsoft.CmdPal.UI/Helpers/Icons/IconServiceRegistration.cs

@@ -36,6 +36,10 @@ internal static class IconServiceRegistration
             WellKnownIconSize.Size256,
             (_, _) => new CachedIconSourceProvider(loader, 256, 64));
 
+        services.AddKeyedSingleton<IIconSourceProvider>(
+            WellKnownIconSize.Unbound,
+            (_, _) => new IconSourceProvider(loader, IconLoaderService.NoResize, isPriority: true));
+
         return services;
     }
 }

src/modules/cmdpal/Microsoft.CmdPal.UI/Helpers/Icons/IconSourceProvider.cs

@@ -12,15 +12,17 @@ internal sealed class IconSourceProvider : IIconSourceProvider
 {
     private readonly IconLoaderService _loader;
     private readonly Size _iconSize;
+    private readonly bool _isPriority;
 
-    public IconSourceProvider(IconLoaderService loader, Size iconSize)
+    public IconSourceProvider(IconLoaderService loader, Size iconSize, bool isPriority = false)
     {
         _loader = loader;
         _iconSize = iconSize;
+        _isPriority = isPriority;
     }
 
-    public IconSourceProvider(IconLoaderService loader, int iconSize)
-        : this(loader, new Size(iconSize, iconSize))
+    public IconSourceProvider(IconLoaderService loader, int iconSize, bool isPriority = false)
+        : this(loader, new Size(iconSize, iconSize), isPriority)
     {
     }
 
@@ -34,7 +36,8 @@ internal sealed class IconSourceProvider : IIconSourceProvider
             icon.Data?.Unsafe,
             _iconSize,
             scale,
-            tcs);
+            tcs,
+            _isPriority ? IconLoadPriority.High : IconLoadPriority.Low);
 
         return tcs.Task;
     }

src/modules/cmdpal/Microsoft.CmdPal.UI/Helpers/Icons/WellKnownIconSize.cs

@@ -11,4 +11,5 @@ internal enum WellKnownIconSize
     Size32 = 32,
     Size64 = 64,
     Size256 = 256,
+    Unbound = -1,
 }