[TIMOB-19593] Windows: Track native API wrapper conversion objects

We automatically will wrap/unwrap native UI elements to interact with Ti.UI.View and its subclasses. The issue is that we dynamically unwrap the native Windows.UI.Xaml.UIElement and then wrap it in a special subclass of Ti.UI.View without tracking the two objects. So if we say add a native TextBlock to a Ti.Ui.Window - that will generate a one-time dynamic Ti.Ui.View to wrap the TextBlock. If we make other calls that require converting, we'll generate a _new_ converted Ti.UI.View rather than re-use the previously generated one.

win.add(textblock); // will auto convert the TitaniumWindows::UI::Xaml::TextBlock to a TitaniumWindows::UI::View holding the same underlying Windows::UI::Xaml::TextBlock object.
win.remove(textblock); // This likely won't work. We'll generate _another_ dynamic TitaniumWindows::UI::View object rather than lookup the one we generated above.
// We'd probably have to do:
// win.remove(win.children[win.children.length]);