[FrameworkBundle] check if the Validator component is present when forms are enabled

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        | 

The `Symfony\Component\Validator\Validation` class is used in the
`FrameworkExtension` class. Therefore, it is required to have the
Validator component installed in production as well but not only when
being in a development environment.