[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.
IMHO, appended commands should be appended to the line after piped and redirects.
Because, if y want to execute `cmd1 ; cmd2 | cmd3` I can use
```php
new Command('cmd1')
  ->append(new Command('cmd2')->pipe(new Command('cmd3')));
```

But if I want execute `cmd1 | cmd3; cmd2` and run 
```php
new Command('cmd1')
  ->append(new Command('cmd2'))
  ->pipe(new Command('cmd3'));
```
It will not works