Reuse type classes with the same definition

[amir-arad]

This optimization seems necessary for generic types, as a runtime reference creates a new type instance every time.

Most glaring example:

const list = Mutable.List.of(core3.String)();

So every time this code is called (imagine a loop... 😢 ), you'll create a new type definition.

perhaps only for derived types (of, nullable, withDefault etc.)