Inconsistent Windows.UI.Xaml.Interop.TypeName behavior

Describe the bug

I came across this as a sudden whim. I discovered that you can actually construct (or better say implicitly convert) a Windows.UI.Xaml.Interop from a string. If you have a viewmodel like this

    runtimeclass ViewModel
    {
        ViewModel();
        Windows.UI.Xaml.Interop.TypeName MyType;
    }

You can actually assign MyType in xaml using a string, something like

        <Button>
            <Button.DataContext>
                <local:ViewModel MyType="local:MainWindow" />
            </Button.DataContext>
        </Button>

If you put a breakpoint in the setter function, you can actually see the TypeName fields are correctly set.

---

However, if you tried to explicitly construct it, it causes a runtime crash (curiously it compiles):

xmlns:interop="using:Windows.UI.Xaml.Interop" ...
        <Button>
            <Button.DataContext>
                <local:ViewModel>
                    <local:ViewModel.MyType>
                        <interop:TypeName>local:MainWindow</interop:TypeName>
                    </local:ViewModel.MyType>
                </local:ViewModel>
            </Button.DataContext>
        </Button>

Which is the "inconsistent" I am talking about, because something that is implicitly constructed from a string, should also be able to explicitly constructed from a string

Why is this important?

The behavior should be consistent.

Steps to reproduce the bug

As OP.

Actual behavior

No response

Expected behavior

No response

Screenshots

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NuGet package version

WinUI 3 - Windows App SDK 1.8.5: 1.8.260209005

Windows version

Windows 10 (1809): Build 17763

Additional context

No response

The issue names no source files, tests, or entry points. Start by reproducing the implicit string assignment and explicit Windows.UI.Xaml.Interop.TypeName construction from the two XAML snippets on Windows App SDK 1.8.5; done means the explicit form no longer crashes and behaves consistently with the implicit form.