adding dp prototype

[stevenbrix]

prototype for how we can model dependency properties after Published via a property wrapper. At the same time, also using the Swift typesystem to ensure Style's and Setters are constructed properly

a few things on the design:

1. In order to properly subscribe to events, we need access to self in the property wrappers projectedValue. As far as i can tell, there is no way to do this. And since I cannot access self inline with the definition of the property, i have to initialize the wrapper in the initializer of the classes.
2. Style and Setter are generic so that we can specialize who they are applied to. However, there are properties in WinUI which take a type-erased Style type. There is no compile-time validation that you are applying the correct style to an object. However, the WinUI runtime does do this at the time that the property is set.

See the readme and tests for usage