- Now that binary libraries are decompiled to stubs instead of PSI
files, we cannot collect sealed inheritors from `KtFile`s anymore.
Since all `KtFile`s and binary library stubs are both indexed by the
declaration provider, we can collect inheritors from its index
instead.
- Invalidating all sessions at the end of `prepareSealedClassInheritors`
fixes some improper resolve phases in lazy resolution test data. While
the previous implementation requested an uncached resolve session, it
didn't account for sessions of dependencies still being cached.
^KT-65960