Ruby: Take overrides into account for singleton methods defined on modules

[hvitved]

We were previously not handling cases like this:

class A
    def self.singleton; end
end

class B < A
end
B.singleton # should resolve to B#singleton

class C < A
    def self.singleton; end
end
C.singleton # should resolve to C#singleton

DCA shows 20k new call edges, and those I sampled looked legit.

[asgerf]

LGTM with a minor comment

Related to our previous discussion, I noticed some of the new call edges are calls to user-defined new methods.

[asgerf]

Could you add some QLDoc indicating that this takes inheritance into account, and likewise on singletonMethodOnModule.

I'd probably have named these predicates in a way that clarifies their relationship, such as:

• lookupOwnSingletonMethod
• lookupSingletonMethod

[hvitved]

I simply used the naming after the existing lookupMethod predicate for instance methods. I'll add ql doc.