Fix signature clash problems caused by special built-ins

Do not treat members with already changed signature as a reason
to create a hidden copy

See tests for clarification:
- There are `charAt` method in B that has different name in Kotlin - `get`,
  i.e. relevant descriptor has initialSignatureDescriptor != null
- When collecting methods from supertypes, `charAt` from A is also get
  transformed to `get`
- So it has effectively the same signature as B.get (already declared)
- If by an accident B.get had been declared with Kotlin signature
  we would have add A.charAt (after transformation) with special flag:
  HiddenToOvercomeSignatureClash (hides it from resolution)
- But here B.charAt was artificially changed to `get`, so no signature clash
  actually happened

 #KT-13730 Fixed

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassMemberScope.kt

@@ -346,7 +346,7 @@ class LazyJavaClassMemberScope(
             specialBuiltin: CallableDescriptor,
             alreadyDeclaredFunctions: Collection<SimpleFunctionDescriptor>
     ): SimpleFunctionDescriptor =
-        if (alreadyDeclaredFunctions.none { this != it && it.doesOverride(specialBuiltin) })
+        if (alreadyDeclaredFunctions.none { this != it && it.initialSignatureDescriptor == null && it.doesOverride(specialBuiltin) })
             this
         else
             newCopyBuilder().setHiddenToOvercomeSignatureClash().build()!!