Improve overloadings check in generated code

[EgorkaKulikov]

Description

Method ClassId.allMethods and its usage in codegen requires refactoring

Expected behavior

For now, to check functions overloadings and cast null arguments to their types in case we have overloadings with the same number of parameters, we filter all declared methods from class and all its ancestors. But actually, it is the wrong way because we count not only overloadings but overridings too. So, we should filter overloadings before.

Context

Migrated from Jira, issue 1458.