[ExpressionLanguage] way to use getters for private attributes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | No
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        |  

This patch uses the PropertyAccess component in order to use getter strategy when private attribute is read:

```php
class User {
    private $age = 27;
    
    public function getAge()
    {
        return $this->age;
    }
}

$language = new \Symfony\Component\ExpressionLanguage\ExpressionLanguage();
$language->evaluate('user.age > 10', ['user' => new User]); // true
```