wasi-common: windows poll_oneoff implementation is poorly understood

The implementation of WASI `poll_oneoff` on Windows in `wasi-cap-std-sync` (and now copied in `wasi-tokio`) is poorly understood and possibly buggy. It passes the test suite, but we expect that its behavior diverges from the unix implementation in some cases. We should consider refactoring or rewriting it when time permits. This task requires some Windows programming expertise that I don't currently have.

The current implementation is one of the few pieces of pre-rewrite (#2487) wasi-common still around, originally written by @kubkon and others.