[Pitch #2] Structured Concurrency

I posted my thoughts in the other thread about @Lantua’s suggestions re. task control (specifically cancellation). TL;DR: I don’t believe we need Task.Handle or “all” Task functionality in the continuation APIs: those serve to control a task form the outside, but here we’re “inside” a task. Specifically for cancellation, I think we need isTaskCancelled and to be able to install a taskCancellationHandler.