Modeling about swiftui-kit

[Nef10]

I agree that we should have a better way than all this #if os() in the middle of the code.

We also should come up with a good way to handle the different modifiers. E.g. in the ProgressView has a CircularProgressViewStyle which we only show on watchOS, although it is available on all Platforms. We don't show it because on the other platforms it is the default style.

[ivanglushko]

What if you were to use Modules for each platform? That way it won't be messy and shared code (views) can be shared and reused. But it needs a little hustle to implement.