ClassLike Interface

[dantleech]

Similar to #162. Would it make sense to implement a ClassLike interface for ClassDeclaration, InterfaceDeclaration and TraitDeclaration ?

[roblourens]

Yes, I think so. That kind of check does show up in several places like here https://github.com/felixfbecker/php-language-server/blob/master/src/DefinitionResolver.php#L1104.