[WIP] [Form] GroupSequenceProvider 

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [no]
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

When working with the GroupSequenceProvider I discovered a strange behavior when returning multiple groups. It seems that only the first group is being validated.

To describe the issue I added a failing test. Is this intended behavior?