Add testing for our WinRT-specific marshalers

[jkoritzinsky]

We currently don't have any automated tests for our WinRT marshalling. Using the System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeImportAttribute pseduo-attribute, we can mark specific types within an assembly as Windows-Runtime types and make them use WinRT marshalling semantics without needing reg-free WinRT support. This pseudo-attribute is used within System.Runtime.WindowsRuntime in CoreFX to implement WinRT marshalling helpers.

We should use this feature to add some automated testing for the WinRT marshalling within CoreCLR.

Marshalers to test:

• System.Nullable<T> -> Windows.Foundation.IReference<T>
• System.Type -> Windows.UI.DirectUI.Xaml.TypeNameNative
• System.Exception -> HRESULT
• System.Collections.Generic.KeyValuePair<K,V> -> Windows.Foundation.Collections.IKeyValuePair<K,V>
• System.Uri -> Windows.Foundation.Uri
• System.ComponentModel.INotifyPropertyChanged and family
• System.Collections.Specialized.INotifyCollectionChanged and family
• Hidden-length arrays (implicit length parameter in signature after the array)
• WinRT Delegates

[jkoritzinsky]

cc: @AaronRobinsonMSFT

[jkoritzinsky]

Marking this as blocked since we're blocked on moving completely off Jenkins for Windows builds before we can merge in dotnet/coreclr#23529

[jkoritzinsky]

All that's left here is doing the reverse marshalling direction and delegates. I need to decide how I want to do the rest of these tests.

[AaronRobinsonMSFT]

Closing since WinRT support was removed - see #36715.