Support dynamic select

[Kuniwak]

This PR allows select to accept an array of channels. Previously, there was no way to select an array of channels. This PR only modifies functions related to resultBuilders, so the behavior of the channels will remain unchanged.

[Kuniwak]

I found a mistake, so I am moving it back to draft.

[Kuniwak]

I fixed the mistake.

[gh123man]

Hey! Thanks for the contribution. This is a super interesting change and seems like a good addition to the library.

I have a couple of suggestions:

1. What do you think about calling forEach any instead?

forEach implies an operation occurs for each element - however since select will choose only one operation per call, perhaps any would make more sense since select will chose "any one" channel based on it's availability.

ex:

 await select {
      any([a, b]) {
          receive($0) { await result <- $0! }
      }
  }

2. I think an overload to accept variadic parameters would compliment this change. ex:

public func any<T>(_ elements: T..., @SelectCollector cases: (T) -> ([SelectHandler])) -> [SelectHandler] {
    return elements.flatMap { cases($0) }
}

would allow us to also perform an operation like this

 await select {
    any(a, b) {
        receive($0) { await result <- $0! }
    }
}

let me know your thoughts.

[Kuniwak]

What do you think about calling forEach any instead?

Sounds good. any is better, as you suggested. I renamed it at 2f00850.

I think an overload to accept variadic parameters would complement this change

Also, I agreed. I added it at 9217527.

[gh123man]

Looks great. I'm going to merge this, do some additional testing, and publish this in the next release. Thanks again!