[2.3][Form] Dereferenced Form::&all() since it is not supported for PHP <= 5.3.3

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

see 00bc2708bce4f1c16a77c371de871c922c31079 and #8851