[Process][2.2] Fix #8970 : read output once the process is finished, enable pipe tests on Windows

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8970
| License       | MIT

This fix the read of file handles after `proc_close` as described in the issue. I enable some stdin=>stdout pipes tests on windows with some dedicated buffer size. Solving the issue, I finally reproduced this [PHP bug](https://bugs.php.net/bug.php?id=65650) that I first described in my PR note in #8924

Most of Windows usage should be okay, but in case of a program throws lots of output and fills the buffer, some data might be lost/corrupted. Should it be documented ? This is a Windows only known issue.