Composite tasks do not notify parent composites

WhenAllTask and WhenAnyTask mark themselves complete, but do not notify their parent composite.

This means the following orchestration does not resume when all activities complete:

all_task = task.when_all(activity_tasks)
winner = yield task.when_any([cancel_task, all_task])

A current workaround is to wait for each leaf task with repeated when_any calls. The workaround preserves cancellation, but Durable Task Scheduler no longer shows the standard Fan-out group.

Could composite completion propagate to the parent in the same way that CompletableTask.complete() does?

A regression test can compose when_any([cancel, when_all([a, b])]), complete a and b, and verify that the outer task completes with the inner when_all task.

先阅读 WhenAllTask 和 WhenAnyTask，然后将它们的完成行为与 CompletableTask.complete() 进行比较。为 issue 中描述的 when_any([cancel, when_all([a, b])]) 添加回归测试；done 表示完成 a 和 b 会使外部 task 与内部的 when_all task 一起完成。