feat: require all files that import nexus

[Weakky]

closes #823

• feat: removes the graphql.ts and graphql/ convention for schema modules. Instead, nexus parses all the files resolved by typescript (based on the tsconfig.json) and looks for imports to nexus. If nexus is imported, that file will be both required in dev and in the final build production.
• fix: properly updates the dev start module when there are layout changes so that new/deleted files get/don't get imported

Status: Waiting for discussion/approval before updating docs

TODO

• docs
• tests

[jasonkuhrt]

Let's make sure to do a pass on the schema guide (if needed) and the "project layout" docs section. Also maybe the @nexus/schema migration guide. Other than that, I don't think any other sections need revising. 🤔

[jasonkuhrt]

So now before every restart the hook allows altering what entrypoint source is? Cool

[Weakky]

Yeah. Makes me think it's dangerous to expose that on the plugin interface. Here, what this specifically enables is the ability to refresh the required schema modules in the start module whenever a file changes.

This used to not be required because we were looking for schema modules based on the filenames. So recomputing the layout whenever a file was added/deleted was enough.

But now that we find schema modules based on their import to Nexus, we need to recompute that on every file change. Here's a simple use-case where this is needed:

1. You create a file (that file is still not considered a nexus module)
2. You add import { schema } from 'nexus'
3. The start module needs to be updated to contain a require to that file
4. You comment out the import to nexus from that file
5. The start module needs to be updated to no longer contain a require to that file

See, nexus modules are no longer tied to file creation/deletion anymore, but entirely based on their content

[jasonkuhrt]

@Weakky once you wrap with #866 let's loop back asap to this one and get it over the finish line. IIRC its just some doc and tests.