Previously, Windows would always defer event processing to the loop
after they were received. This could cause confusion for users who were
using prepare and idle callbacks, as seen from this bug in nodejs[^1] and
this discussion in libuv[^2], and even some discrepancies in the libuv
tests too[^3].
[^1]: https://github.com/nodejs/node/pull/42340
[^2]: https://github.com/libuv/libuv/discussions/3550
[^3]: See change to test-spawn.c in this PR
So rather than declare those usages to be wrong, we change libuv to meet
those users expectations.
Replaces: https://github.com/libuv/libuv/pull/3585
ee3718dd71