Under COMPOSITE mode we don't have a globally known way to create
built-ins, instead, we have to create them on per-module basis.
So, in this commit we:
1. Use builtInsProvider: (ModuleInfo) -> KotlinBuiltIns instead of
precomputed builtIns instance, in order to be able to calculate
builtIns on per-module basis
2. Introduce new entity, called BuiltInsCache, which, roughly
speaking, is a map of form ModuleInfo -> KotlinBuiltIns, to prevent
creation of multiple builtInsInstances
NB. Actually, it's of form BuiltInsCacheKey -> KotlinBuiltIns, because
we shouldn't create new builtIns for each module. Also, currently,
each platform has its own BuiltInsCacheKey implementation, because
parameters by which built-ins are created, are a bit different across
different platforms. Ideally, we should eliminate those differences
and they use one concrete implementation as a key.
Dmitry Savvinov
2b4d70fcf0