Fix Document editor with "use client" for getContext in NextJS App Directory

[borisno2]

Currently, if you add the document field to a project and use getContext in the NextJs app directory, the next build will fail due to how the document editor validates the schema on the server side - the result being useState in a server-side component. This PR marks two files with "use client" so Next knows these are client-side files.

Thanks to @gautamsi for working this one out - see comment on #8371

[dcousens]

LGTM, though I wonder how scalable this is for nextjs@13 if you need upstream libraries to add directives

[borisno2]

This is failing due to preconstruct and rollup bundling files together where Module Level directives are ignored. That makes this approach not achievable.

The root cause of this is the crossover of React/Next code in the getContext - in the document field case, this is used for validation of the JSON object to stop runtime errors in the frontend (Keystone effectively renders the Document Editor on the backend to parse and validate the JSON). Ideally, the root cause of this needs to be resolved - remove the need for and decouple the Admin UI (Studio) from the API framework (getContext) this will also help with reducing the weight of keystone when using getContext

Closing this PR, while we continue to explore this use case in #8371

[borisno2]

Giving this another go in light of the latest preconstruct release #8423

[gautamsi]

great to see this back, please release soon :)