[Process] Add support for streams as input

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8161
| License       | MIT

`Process::setStdin` now accepts a stream as input.
I've also split windows and unix pipes management.