Add special handling of `schema.graphql` files

[lemonmade]

Would be great to be able to import from a schema.graphql/ X.schema.graphql file, and automatically get:

• An export with the source of the schema
• An export of the GraphQL schema (maybe?)
• An export of the types in the schema

Today, we have some ok-ish stuff that exports the types of the schema and the source, but you have to designate a custom .ts file to export to, so you don't import from the actual .graphql file.