Add type to importing of Object interfaces

[jhugman]

According to The Big O of Code Reviews, this is a O(n) change.

Fixes #81.

This PR adds type to the imports of types between crates, and reviews what uniffi types should be imported as consts and which as types.

Before:

import { 
  MyObjectInterface, 
  MyCallbackInterface, 
  MyEnum, 
  type MyRecord 
} from "./other-crate"

Now:

import { 
  type MyObjectInterface, 
  type MyCallbackInterface, 
  MyEnum, 
  type MyRecord 
} from "./other-crate"

It also adds a playground test in the testing directory.