[Php81][Restoration] Handle crash on ReadOnlyPropertyRector+MakeTypedPropertyNullableIfCheckedRector

[samsonasik]

Given the following code:

final class SomeClass
{
    private AnotherClass $anotherClass;

    public function run()
    {
        if ($this->anotherClass === null) {
            return null;
        }
    }
}

It changed to:

-private AnotherClass $anotherClass;
+private readonly ?AnotherClass $anotherClass = null;

which nullable property can't be readonly, and immediatelly cause fatal error:

Fatal error: Readonly property SomeClass::$anotherClass cannot have default value

see https://3v4l.org/3RBpN

Applied rules:

Rector\Php81\Rector\Property\ReadOnlyPropertyRector
Rector\Restoration\Rector\Property\MakeTypedPropertyNullableIfCheckedRector

This PR try to fix it.

Fixes rectorphp/rector#7590

[samsonasik]

Fixed 🎉 /cc @Wohlie

[samsonasik]

All checks have passed 🎉 @TomasVotruba it is ready for review.

[TomasVotruba]

Thank you 👍