Before this change generic signature wasn't written because of wrong
assumption about it absence in all cases where we replace generic parameter
with Object
By default we would render 'MutableCollection<String>.addAll(Collection<String>)' as
'(LCollection<String>;)' (without wildcard) because String is final and
effectively it's the same as '(LCollection<? extends String>;)'.
But that's wrong signature in a sense that java.util.Collection has different
signature: '(LCollection<? extends E>)'.
Actually the problem is much wider than collections,
it concerns any Java code that uses Kotlin classes with covariant
parameters without '? extends E' wildcards.
Temporary solution is just to hardcode/enumerate builtin methods
with special signature.
Of course not only for contains but for other methods having INSTANCEOF bar.rier
Otherwise using platform null values becomes for such methods becomes
dangerous in cases like `platformString in setOf("", "")`
Denis Zharkov