syscall: introduce SysProcAttr.AdditionalInheritedHandles on Windows

This allows users to specify handles that they explicitly want to be
inherited by the new process. These handles must already be marked as
inheritable.

Updates #44011.
Updates #21085.

Change-Id: Ib18322e7dc2909e68c4209e80385492804fa15d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/288298


Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>