When a language feature has UNSTABLE_FEATURE kind, enabling it causes
the compiler to mark the compiled library with the pre-release flag.
JsAllowValueClassesInExternals feature is enabled by default in JS IR
backend. So effectively, all JS klibs are marked with the pre-release
flag. This remained unnoticed because the compiler currently doesn't
read this flag from klibs. This will change soon.
To fix the problem, this commit changes the feature kind to OTHER, which
doesn't enforce the pre-release flag.
Svyatoslav Scherbina
4db7bac4c0