- Materialize unit when its value is actually needed.
- Special-case Unit_getInstance return type at codegen. It should be a
proper Unit object instead of a "void"
Without this commit, JVM name mapping logic in BE does not work for FIR,
because FIR cannot use old BuiltInsPackageFragmentImpl descriptor.
In this commit we add our own implementation thus fixing
a pack of FIR black box tests.
Svyatoslav Kuzmich