TypeScript shared type packaging

[mdekrey]

Currently, only a single version of @principlestudios/openapi-codegen-typescript can be used in a project because the generated types reference the project directly.

Options:

1. Consider moving TS dependencies into generated output instead of the shared library for better side-by-side support of other versions of the generator. TS has to work much harder to detect types if packaged with the adapter layers - it doesn't succeed even with the exact same type definitions. This seems like a non-starter.
2. For generation, allow customization of the package where the typings and helpers are found. This could be a command-line switch.