[Process] Add support for streams as input
feature #10934 [Process] Add support for streams as input (romainneutron)

This PR was squashed before being merged into the 2.6-dev branch (closes #10934).

Discussion
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[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.

Commits
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b57024e [Process] Add support for streams as input