[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.
If you have both appended and piped, only last appended will be piped (same for redirects).
Should be 
`return implode(' ', $this->parts).($this->piped ? ' | '.$this->piped : '').$this->getredirects().implode('; ', $this->appended)`