[To discuss] Explain the difference between arithmetic- and storage- primitive types

It would be nice to explain and provide recommendations regarding usages of various types in public API.

The overall recommendations should make a clear distinction between _arithmetic_ types (e.g. `Int`, `Long` and `Double`, ones that folks do arithmetics around) and _storage_ types (e.g. `Short`, `Byte`, `Float`, ones that are rather a memory layout optimization), as well as provide a recommendation *what* should be used in public's API and *why*
~Also let's deprecate `Char` while we are here~

The issue names no specific file or test; start by reviewing the existing API-guidelines documentation and its treatment of Kotlin primitive types. Done means documenting the distinction between arithmetic and storage types, with recommendations for public APIs and reasons for those recommendations.

Written by the indexing model from the issue text.