Previoisly, there were two places where mapping had happened:
- toConeKotlinTypeWithNullability
- enhancePossiblyFlexible
The first one was used for supertypes and bounds and the second one
was used for other signature parts
The main idea is to perform type mapping once to a flexible type,
and then use it as it's needed (it's lower bound, or for the further ehnancement)
Also, this commit fixes flexibility for type arguments, see the tests
Dmitriy Novozhilov