DesktopAttachedSiteBridge and DesktopPopupSiteBridge don't inherit from DesktopSiteBridge

Describe the bug

DesktopAttachedSiteBridge and DesktopPopupSiteBridge don't inherit from DesktopSiteBridge, causing crashes in Input, which affects flyouts in XAML as it tries to get a DesktopSiteBridge and failing.

Steps to reproduce the bug

Sample code:

Microsoft.UI.Xaml.XamlIsland island = new();

Microsoft.UI.Xaml.Controls.Button but = new() { Content = "Test" };
Microsoft.UI.Xaml.Controls.MenuFlyout flyout = new();
flyout.Items.Add(new Microsoft.UI.Xaml.Controls.MenuFlyoutItem() { Text = "Test 1" });
flyout.Items.Add(new Microsoft.UI.Xaml.Controls.MenuFlyoutItem() { Text = "Test 2" });
flyout.Items.Add(new Microsoft.UI.Xaml.Controls.MenuFlyoutItem() { Text = "Test 3" });
flyout.ShouldConstrainToRootBounds = false;
but.Flyout = flyout;

island.Content = but;

Microsoft.UI.Windowing.AppWindow appWindow = Microsoft.UI.Windowing.AppWindow.Create();
appWindow.Show();

DesktopAttachedSiteBridge siteBridge = DesktopAttachedSiteBridge.CreateFromWindowId(appWindow.Id);
child.Connect(island.ContentIsland);

Clicking on the button while running under a debugger will reveal that it crashes at Microsoft_UI_Input!ContentIsland::Partner::get_TEMP_DesktopSiteBridge

Expected behavior

Both classes should inherit from DesktopSiteBridge.

Screenshots

No response

NuGet package version

Windows App SDK 1.7.0: 1.7.250310001

Packaging type

Packaged (MSIX)

Windows version

Insider Build (xxxxx)

IDE

Visual Studio 2022-preview

Additional context

No response

Start by locating the definitions of DesktopAttachedSiteBridge, DesktopPopupSiteBridge, and DesktopSiteBridge, then reproduce the flyout crash at ContentIsland::Partner::get_TEMP_DesktopSiteBridge using the provided sample. Confirm that both attached and popup bridge types inherit from DesktopSiteBridge and that the sample no longer crashes when interacting with the MenuFlyout.