Add a way to write and reference generated types

[peterp]

We're trying to make the magic we introduce via Babel less magical to TypeScript. This PR gives us the ability to generates types in node_modules/@types/@redwoodjs which are automatically imported by TypeScript.

• Generate types for import-dir.
• Generate types for Routers routes.<routeName>()
• Generate types for Pages

[peterp]

Here's an example of the generated routes:

[peterp]

Here's an example of the generated directory imports

[peterp]

Here's an example of a type definition for an auto-page import