Previously, it was obtained from expected type of a variable being assigned,
but it's better to use the type of resulting expression
Initially this part was brought in 4ab0897d7d,
but as we see in commit message and tests it was all about unit-coercion
- Add utilities to add new attribute to ConeAttributes
- Get rid of FlexibleNullability attribute (it can be easily inferred
for any flexible type at any moment)
- Fix determining of EnhancedNullability attribute
Vladimir Sukharev