Call RegisterXamlHostComponentView on demand

RegisterXamlHostComponentView internally calls the costly WindowsXamlManager.InitializeForCurrentThread function. This function call should precede any XAML-based calls.

This is not called today so no 3P modules will run without it. It can't be called by default as it'd mean penalizing all RNW apps, even the ones not needing XAML-based components.

Call this at the registration of the first XAML-based component an app imports.