Match SwiftUI `Image` modifiers

[MaxDesiatov]

I think to match some of SwiftUI's Image modifiers we'll need to implement the internal storage as an AnyTokenBox. Then once we add support for things like template images we can access the environment to render them.

Originally posted by @carson-katri in https://github.com/TokamakUI/Tokamak/pull/155#discussion_r533775894