[Pitch] Enable pack iteration

Evolution Pitches
3

I want to do something like this, is it possible?

func allUnwrapOrNil<each Element>(over element: repeat (each Element)?) -> (repeat each Element)? {
  let result: (repeat each Element)
  for (value, resultTarget) in repeat (each element, each result) {
    guard let value else {
      return nil
    }
    resultTarget = value
  }
  return result
}

This can be just a bikeshedding, but I think generalized repeat syntax instead of for ... in can be a good alternative.

func == <each Element: Equatable>(lhs: (repeat each Element), rhs: (repeat each Element)) -> Bool {
  repeat {
    guard each lhs == each rhs else { return false }
  }
  return true
}

This way, current repeat each element can be considered 'expression' version of repeat statement, which makes much consistency with if and switch.