Revisit types exported from the SDK

[sodic]

Item 47 of Effective Typescript says "Export all types that appear in public APIs. The reasoning is solid and goes something like this:

Users will eventually want to reference a type your library uses (e.g., it's part of a function's type signature) only to find out it isn't exported. Since TypeScript has many powerful utility types, they'll find a way to extract and use it anyway (e.g., with ReturnType, Parameters, typeof, etc.).

If a type appears in a public function declaration, it's effectively exported. Therefore, you should do your users a favor and just export them explicitly.

Our SDK doesn't currently do this, so let's make it happen :)