Add support for attribute accessors without return type declared in closures

[EmanueleCoppola]

Summary

Enable the recognition of attributes without any return type in the declared closures.

The following example was not recognized before:

protected function attributeWithoutReturnTypes(): Attribute
{
    return new Attribute(
        function (?string $name) {
            return $name;
        },
        function (?string $name) {
            return $name === null ? null : ucfirst($name);
        }
    );
}

Now the aforementioned method should produce the following declaration:

 * @property mixed $attribute_without_return_types

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• Existing tests have been adapted and/or new tests have been added
• Add a CHANGELOG.md entry
• Update the README.md
• Code style has been fixed via composer fix-style

[mfn]

What was returned before?

[EmanueleCoppola]

Before it didn't even show the attribute

[barryvdh]

Is this fixed with #1411 ?