Fix: reopen async File passed to Process.exec and .run (win32)

[ysbaddaden]

The arguments for input, output and error must be handles without FILE_FLAG_OVERLAPPED so we can't pass a File opened with blocking: false... but we can reopen the file from its #path using ReOpenFile as blocking.

This feels more like a hack than a proper solution. I initially tried ReOpenFile, but I couldn't get it to work, while the crude hack just worked 🤷

This is working as long as the file isn't closed, in which case we can just use the current file handle: we can pass an async closed handle (but can't reopen a closed file).

Extracted from #15685

[ysbaddaden]

I tried ReOpenFile again. I did something wrong previously, like trying to reopen non-File handles, because now it appears to work correctly.

See e351e6c in #15685. Let's see if CI succeeds for the PoC.

[ysbaddaden]

Updated to use ReOpenFile.