State vars have to be first

[j-f1]

If any non-state variables precede state variables, Tokamak crashes when the state variables are read.

Repro:

struct ThisView: View {
  let foo = 3
  @State var bar = 4

  @ViewBuilder var body: some View {
    Text("\(bar)")
  }
}

Encountered in #129.

This happens because StackReconciler#render(compositeView:) enumerates all the properties, resulting in it providing non-consecutive ids to setupState. A potential fix is to declare a var stateIdx outside of the loop and manually increment it when initializing each state variable.

https://github.com/swiftwasm/Tokamak/blob/ffa686c7dca8d454e88246ed2ba7106dee6c4836/Sources/TokamakCore/StackReconciler.swift#L115-L121

[MaxDesiatov]

The proposed fix seems totally legit, let me know if you're submitting a PR for it, otherwise I'll pick it up soon-ish.