Fix WinRT marshalling for NotifyPropertyChangedEventArgs and NotifyCollectionChangedEventArgs (CoreCLR side) (#23401)
* Enable marshalling IntPtr and UIntPtr in WinRT scenarios to support our marshalling infrastructure.
* Enable getting an RCW for a native COM object while ignoring WinRT projections.
* Rename to Marshal.GetUniqueObjectForIUnknownWithoutUnboxing
* Clean up contract.
* Move GetUniqueObjectForIUnknownWithoutUnboxing to WindowsRuntimeMarshal.
* Move WinRT-specific FCalls to WindowsRuntimeMarshal.