Introduce Flow.any, Flow.all, Flow.none

[CLOVIS-AI]

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As discussed in #4212.

This is my first proper contribution to Coroutines, so please be nice :)

At this stage, my goals are: • Optimal API surface • Correctness

I have not made any attempts to improve performance. In particular, I wouldn't be surprised if any could be improved. I believe all and none are optimal.

[CLOVIS-AI]

I took inspiration from other tests, which seem to use expect(Int) and finish(Int), but I'm not completely sure what they're for nor how to use them, so I didn't. Please let me know if they are necessary.

[qwwdfsad]

@CLOVIS-AI would you like to continue this PR or should we handle it from here?

[CLOVIS-AI]

I would love to, but sadly my schedule doesn't allow me too… Feel free to make the changes you want if I'm too slow :)

[dkhalanskyjb]

Closed in favor of #4304