Treat Kotlin code as null-unmarked #209
Description
Obviously it would then be a nice addition to read the nullness information from the @kotlin.Metadata annotation, but it's possible that https://youtrack.jetbrains.com/issue/KT-47417/Emit-jspecify-annotations-for-types-in-Kotlin-binaries will happen before we get around to it, in which case we wouldn't need to.