CmdPal: Add a dock (#45824)

Add support for a "dock" window in CmdPal. The dock is a toolbar powered
by the `APPBAR` APIs. This gives you a persistent region to display
commands for quick shortcuts or glanceable widgets.

The dock can be pinned to any side of the screen.
The dock can be independently styled with any of the theming controls
cmdpal already has
The dock has three "regions" to pin to - the "start", the "center", and
the "end".
Elements on the dock are grouped as "bands", which contains a set of
"items". Each "band" is one atomic unit. For example, the Media Player
extension produces 4 items, but one _band_.
The dock has only one size (for now)
The dock will only appear on your primary display (for now)

This PR includes support for pinning arbitrary top-level commands to the
dock - however, we're planning on replacing that with a more universal
ability to pin any command to the dock or top level. (see #45191). This
is at least usable for now.

This is definitely still _even more preview_ than usual PowerToys
features, but it's more than usable. I'd love to get it out there and
start collecting feedback on where to improve next. I'll probably add a
follow-up issue for tracking the remaining bugs & nits.

closes #45201

---------

Co-authored-by: Niels Laute <niels.laute@live.nl>

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Services/DockThemeSnapshot.cs

@@ -0,0 +1,73 @@
+// 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.CmdPal.UI.ViewModels.Settings;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Media;
+using Windows.UI;
+
+namespace Microsoft.CmdPal.UI.ViewModels.Services;
+
+/// <summary>
+/// Represents a snapshot of dock theme-related visual settings, including accent color, theme preference,
+/// backdrop, and background image configuration, for use in rendering the Dock UI.
+/// </summary>
+public sealed class DockThemeSnapshot
+{
+    /// <summary>
+    /// Gets the accent tint color used by the Dock visuals.
+    /// </summary>
+    public required Color Tint { get; init; }
+
+    /// <summary>
+    /// Gets the intensity of the accent tint color (0-1 range).
+    /// </summary>
+    public required float TintIntensity { get; init; }
+
+    /// <summary>
+    /// Gets the configured application theme preference for the Dock.
+    /// </summary>
+    public required ElementTheme Theme { get; init; }
+
+    /// <summary>
+    /// Gets the backdrop type for the Dock.
+    /// </summary>
+    public required DockBackdrop Backdrop { get; init; }
+
+    /// <summary>
+    /// Gets the image source to render as the background, if any.
+    /// </summary>
+    /// <remarks>
+    /// Returns <see langword="null"/> when no background image is configured.
+    /// </remarks>
+    public required ImageSource? BackgroundImageSource { get; init; }
+
+    /// <summary>
+    /// Gets the stretch mode used to lay out the background image.
+    /// </summary>
+    public required Stretch BackgroundImageStretch { get; init; }
+
+    /// <summary>
+    /// Gets the opacity applied to the background image.
+    /// </summary>
+    /// <value>
+    /// A value in the range [0, 1], where 0 is fully transparent and 1 is fully opaque.
+    /// </value>
+    public required double BackgroundImageOpacity { get; init; }
+
+    /// <summary>
+    /// Gets the effective acrylic backdrop parameters based on current settings and theme.
+    /// </summary>
+    public required BackdropParameters BackdropParameters { get; init; }
+
+    /// <summary>
+    /// Gets the blur amount for the background image.
+    /// </summary>
+    public required int BlurAmount { get; init; }
+
+    /// <summary>
+    /// Gets the brightness adjustment for the background (0-1 range).
+    /// </summary>
+    public required float BackgroundBrightness { get; init; }
+}

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Services/IThemeService.cs

@@ -2,6 +2,8 @@
 // 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.CmdPal.UI.ViewModels.Settings;
+
 namespace Microsoft.CmdPal.UI.ViewModels.Services;
 
 /// <summary>
@@ -36,4 +38,9 @@ public interface IThemeService
     /// Gets the current theme settings.
     /// </summary>
     ThemeSnapshot Current { get; }
+
+    /// <summary>
+    /// Gets the current dock theme settings.
+    /// </summary>
+    DockThemeSnapshot CurrentDockTheme { get; }
 }