Split the View trait into View and Widget

[Zoxc]

This splits the View trait into View and Widget. The Widget has all the functionality of the previous View trait while the new View trait has a method to build widgets and necessary access for view decorators. Widget::id is removed as there where common conflicts with View::id as most widgets implement both View and Widget.

AnyView is a new type equivalent to the old Box<dyn View> as the new View trait is no longer object safe so it can't have dynamic dispatch. The View trait has an any method to convert views into AnyView. That seems to be reasonably ergonomic.

DynStack and VirtualStack are changed to use dynamic dispatch for widgets to reduce generic parameters.

This provides a layer of separation between widgets and views which means you can create APIs in a builder pattern style making the final built widget a function of the configured view state. I have yet to look over and see if there's any problems with View::build being called in a different Scope.