Check for inheritance issues when analyzing php 8.2 readonly classes

[TysonAndre]

Phan should warn about invalid inheritance for https://wiki.php.net/rfc/readonly_classes

Related to #4684

php > readonly class B {}
php > class C extends B{}
Fatal error: Non-readonly class C cannot extend readonly class B in php shell code on line 1
php > readonly class D extends stdClass{}
Fatal error: Readonly class D cannot extend non-readonly class stdClass in php shell code on line 1