Switch to state management using reference types

[david-swift]

Steps

• Build the project on your machine. If it does not compile, fix the errors.
• Describe the purpose and approach of your pull request below.
• Submit the pull request. Thank you very much for your contribution!

Purpose

The identifier system using value types only may have a slightly better performance (the difference really seems to be insignificant though), but results in strange behavior in certain situations:

struct Test: View {

    @State private var property1 = false
    @State private var property2 = false

    var view: Body {
        Button("Toggle") {
            property1.toggle()
            property2.toggle() // Nothing happens as the IDs already changed
        }
    }

}

With the reference type approach, the reference to the value will work as long as it exists and not break with the next update.

Approach

Remove StateManager's function of storing state and store state in a decentralized way instead.