Explore using `OwnedHandle`

[acj]

Rust shipped with a stable std::os::windows::io::OwnedHandle (RFC) in 1.63. Let's consider using it as an improved ProcessHandle.

References:

• https://doc.rust-lang.org/std/os/windows/io/struct.OwnedHandle.html
• https://internals.rust-lang.org/t/pre-rfc-i-o-safety/14585
• Cleanup and fix windows handle leak #16
• Implement Deref for ProcessHandle #17
• Switch to windows-sys #21