(TODO message) test
Delete ErrorSimpleFunctionDescriptorImpl and error property

Error scope doesn't have any declarations
Replace some usages of ERROR_CLASS with new instance creation

Because when some class is unresolved, we can still hold some information such
as its FQ name, for debugging purposes and better error messages
(TODO lazy?) Introduce KFunctionImpl, KMemberFunctionImpl, KExtensionFunctionImpl

Old 23*3 classes will be dropped, since they have no value
(TODO merge GenerateFunctions) Delete K*FunctionNImpl classes