Swift 6

Adds support for Swift 6, inheriting actor isolation through the new #isolation keyword (SE-420).

let val: String = await withIdentifiableContinuation { 
  continuations[$0.id] = $0
}

Swift 5 must continuation to pass an isolated reference to the current actor.

let val: String = await withIdentifiableContinuation(isolation: self) { 
  continuations[$0.id] = $0
}