Added to form property closure support

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #4067
| License       | MIT
| Doc PR        | no

Added to form property closure support
Why do you limit this to ``Closure `` instances? ``is_callable()`` seems more sensible to me.