`isSubClassOf` was changed in an earlier commit to use the session of
`subClass` instead, but that approach comes with multiple problems:
- We need to resolve classes from the use-site to take actualization of
`expect` types into account.
- If `superClass` is a builtin and we resolve supertypes from
`subClass`'s session, we may get multiple instances of symbols for the
same builtin from different sessions (i.e. one from a stdlib session
via the use-site session and another from the fallback builtins
provider for binary libraries if `subClass` is from a binary library).
^KT-66013
Marco Pennekamp
9d2298b326