[Form] Fixed Form::all() signature for PHP 5.3.3
merged branch bschussek/dereference-all-2.2 (PR #8851)

This PR was merged into the 2.2 branch.

Discussion
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[2.2][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

Commits
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ea480bd [Form] Fixed Form::all() signature for PHP 5.3.3