[WIP][Process] Add Process\Command

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #10025
| License       | MIT
| Doc PR        | todo

I open a PR for this work-in-progress as an alternative to #11971. The implementation of the Process Command is quite okay, it should be tested and the API validated. 

This Command would help us to enforce the use of the ProcessBuilder and provide a way to avoid command injections.
I wonder if piped should be applied to the original command or the last appended ?
```php
$c = new Command('ls -al');
$c->pipped(new Command('wc -l))
  ->append(new Command('exit $code', false));
```