P6: Fix isAbstract() for unimplemented abstract properties (PHP 8.4)

[devin-ai-integration]

Fix isAbstract() in ReflectionClassLikeTrait for classes with unimplemented abstract properties.

Current implementation only checks $this->classLikeNode->isAbstract() for classes and !empty($this->getMethods()) for interfaces. With PHP 8.4, interfaces can have abstract properties, and a concrete class that doesn't implement them should be considered abstract.

Depends on P4 being merged first.

Part of #162

[devin-ai-integration]

Completed in the PHP 8.3/8.4 parity work (Waves 1-5).