…r class

Fix an issue where inner classes which reference their outer class via a labeled
expression would still be reported as unnecessary. This seems to be due to a
missing visitExpressionWithLabel() check which resolves the label name: if the
label is referencing a parent class, then the nested class must be `inner`.

I wasn't able to find a way to resolve the labeled expression as a ClassId to
match the existing class check from KtReferenceExpression, so I settled for
using the class name instead, which is easy to obtain. This means there's a fair
bit of duplication in overriden checkForOuterUsage() methods to check parent
classes which could probably be removed, but I didn't see a particularly clean
way to do so.

… labeled expressions