General: Review core validators and extension method validators (duplicated behaviour)

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Package/Plugin version

11.0.0

### What you'd like to happen

```Markdown
I think that some core validators could be accomplish with extension methods and viceversa. Maybe can remove some of them.
```

### Alternatives you've considered

```Markdown
Example: skipWhen
I understand that `FormBuilderValidators.skipWhen(validator: FormBuilderValidators.numeric(), condition: (int? value) => value == 0)` is the same that `FormBuilderValidators.numeric().skipWhen(condition: (int? value) => value == 0)`
```

### Aditional information

_No response_