[futures] Add collectAny() to ivalue::Future for completeness (#39597)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39597
To complement collectAll(), this change adds collectAny(), and writes
up relevant unittest coverage.
We also remove the vector-based helper version of collectAll(), which
was debatable usefulness in a previous change.
ghstack-source-id: 105527180
Test Plan: buck test mode/dev-nosan caffe2/test/cpp/jit/...
Differential Revision: D21910311
fbshipit-source-id: dbb3ca404672a3d751b1b3cf016e6084a9ff8040
