Shadows overview sample in gallery crashes under Windows App SDK

[Arlodotexe]

Describe the bug

When running the gallery with the Wasdk head on the latest main commit, the 'Shadows overview' sample will crash the app:

Exception message:

Specified cast is not valid.

Stack trace:

   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|38_0(Int32 hr)
   at ABI.Microsoft.UI.Xaml.IFrameworkElementOverridesMethods.MeasureOverride(IObjectReference _obj, Size availableSize)
   at Microsoft.UI.Xaml.FrameworkElement.MeasureOverride(Size availableSize)
   at Microsoft.UI.Xaml.FrameworkElement.Microsoft.UI.Xaml.IFrameworkElementOverrides.MeasureOverride(Size availableSize)
   at ABI.Microsoft.UI.Xaml.IFrameworkElementOverrides.Do_Abi_MeasureOverride_0(IntPtr thisPtr, Size availableSize, Size* result)

This behavior is not present when running the gallery under UWP.

Steps to reproduce

1. Clone the repo
2. Generate the gallery solution, include the Media component and the wasdk multitarget/head.
3. Build and deploy the wasdk gallery 
4. Navigate to the 'Shadows overview' sample page and observe crash.

Expected behavior

No crash

Screenshots

No response

Code Platform

• [ ] UWP
• [X] WinAppSDK / WinUI 3
• [ ] Web Assembly (WASM)
• [ ] Android
• [ ] iOS
• [ ] MacOS
• [ ] Linux / GTK

Windows Build Number

• [ ] Windows 10 1809 (Build 17763)
• [ ] Windows 10 1903 (Build 18362)
• [ ] Windows 10 1909 (Build 18363)
• [ ] Windows 10 2004 (Build 19041)
• [ ] Windows 10 20H2 (Build 19042)
• [ ] Windows 10 21H1 (Build 19043)
• [ ] Windows 10 21H2 (Build 19044)
• [ ] Windows 10 22H2 (Build 19045)
• [ ] Windows 11 21H2 (Build 22000)
• [ ] Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• [ ] Windows 10, version 1809 (Build 17763)
• [ ] Windows 10, version 1903 (Build 18362)
• [ ] Windows 10, version 1909 (Build 18363)
• [ ] Windows 10, version 2004 (Build 19041)
• [ ] Windows 10, version 2104 (Build 20348)
• [ ] Windows 11, version 22H2 (Build 22000)
• [ ] Other (specify)

Other SDK version

No response

Visual Studio Version

No response

Visual Studio Build Number

No response

Device form factor

No response

Additional context

No response

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[Arlodotexe]

This error only throws when AoT is enabled. Running without AoT works as expected:

Also worth noting that this document doesn't have any embedded samples in it. This means might be an issue with the MarkdownTextBlock being used by the gallery.

[Arlodotexe]

We're still using 7.1.2 for the Markdown renderer in the Gallery:

• tooling/ProjectHeads/App.Head.Uwp.Dependencies.props#L5
• tooling/ProjectHeads/App.Head.WinAppSdk.Dependencies.props#L5.

These will need to be updated to the latest version of MarkdownTextBlock in Labs.