KT-16440 ClassConstructorDescriptorImpl has null returnType

Set constructor return type in FunctionDescriptorResolver#createConstructorDescriptor
(it seems to be the only place where ClassConstructorDescriptorImpl#initialize(...)
is called, but returnType is not set).

compiler/frontend/src/org/jetbrains/kotlin/resolve/FunctionDescriptorResolver.kt

@@ -317,6 +317,7 @@ class FunctionDescriptorResolver(
                         DescriptorUtils.getDefaultConstructorVisibility(classDescriptor)
                 )
         )
+        constructor.returnType = classDescriptor.defaultType
         if (DescriptorUtils.isAnnotationClass(classDescriptor)) {
             CompileTimeConstantUtils.checkConstructorParametersType(valueParameters, trace)
         }