[Process] Deprecate Process::setStdin in favor of Process::setInput

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT

From the `Process` point of view, what we pass is an *input*, as well as we retrieve *output* and *error output*.
As we use `getOutput` and `getErrorOutput` we should use `setInput` and let the underlying `ProcessPipes` deal with the actual `STDIN`.

By the way, `ProcessBuilder` already has `setInput` method and no `setStdin` method