feat: consolidates REST API handling, decouple from next.js (#10466)

This PR improves how we handle REST API.
Problems before:
* `packages/next/src/routes/rest/*` had a huge amount of code that
didn't depend on next.js at all.
* `packages/next/src/routes/rest/index.ts` itself was not only huge but
also really hard to follow. Every method (`GET`, `POST` etc. was almost
full copy of another).
* `packages/next/src/utilities` had some utilities like
`headersWithCors` or `createPayloadRequest` that again, weren't depend
on next.js and potentially can be used outside of next.js.

Now:
All the logic that's not related to next.js now is inside
`packages/payload`, `packages/next/src/routes/rest/index.ts` now is only
_40_ lines instead of 900+
Functions like `headersWithCors` are now implemented and exported in
`payload`. To keep bc, we re-export them from the same path but marked
as `@deprecated`.

You can attach Payload REST API to any backend framework that uses Fetch
API (like Remix / SolidStart / Bun / Hono) if you don't need the admin
panel in your server instance, but you still want to have REST API. The
main function [`handleEndpoints`

](https://github.com/payloadcms/payload/pull/10466/files#diff-82e97630068f9fc40256f3f46e06226215ab150d16012281810586b51b0cfd51R28)
accepts `Request` and returns `Response`.
It's also doable with Express, but you'd have to convert node.js'
req/res to fetch.

Author: r1tsuu

packages/next/src/exports/utilities.ts

@@ -1,8 +1,67 @@
 // NOTICE: Server-only utilities, do not import anything client-side here.
-export { addDataAndFileToRequest } from '../utilities/addDataAndFileToRequest.js'
-export { addLocalesToRequestFromData, sanitizeLocales } from '../utilities/addLocalesToRequest.js'
-export { createPayloadRequest } from '../utilities/createPayloadRequest.js'
+
 export { getNextRequestI18n } from '../utilities/getNextRequestI18n.js'
 export { getPayloadHMR } from '../utilities/getPayloadHMR.js'
-export { headersWithCors } from '../utilities/headersWithCors.js'
-export { mergeHeaders } from '../utilities/mergeHeaders.js'
+
+import {
+  addDataAndFileToRequest as _addDataAndFileToRequest,
+  addLocalesToRequestFromData as _addLocalesToRequestFromData,
+  createPayloadRequest as _createPayloadRequest,
+  headersWithCors as _headersWithCors,
+  mergeHeaders as _mergeHeaders,
+  sanitizeLocales as _sanitizeLocales,
+} from 'payload'
+
+/**
+ * Use:
+ * ```ts
+ * import { mergeHeaders } from 'payload'
+ * ```
+ * @deprecated
+ */
+export const mergeHeaders = _mergeHeaders
+
+/**
+ * @deprecated
+ * Use:
+ * ```ts
+ * import { headersWithCors } from 'payload'
+ * ```
+ */
+export const headersWithCors = _headersWithCors
+
+/**
+ * @deprecated
+ * Use:
+ * ```ts
+ * import { createPayloadRequest } from 'payload'
+ * ```
+ */
+export const createPayloadRequest = _createPayloadRequest
+
+/**
+ * @deprecated
+ * Use:
+ * ```ts
+ * import { addDataAndFileToRequest } from 'payload'
+ * ```
+ */
+export const addDataAndFileToRequest = _addDataAndFileToRequest
+
+/**
+ * @deprecated
+ * Use:
+ * ```ts
+ * import { sanitizeLocales } from 'payload'
+ * ```
+ */
+export const sanitizeLocales = _sanitizeLocales
+
+/**
+ * @deprecated
+ * Use:
+ * ```ts
+ * import { addLocalesToRequestFromData } from 'payload'
+ * ```
+ */
+export const addLocalesToRequestFromData = _addLocalesToRequestFromData

packages/next/src/layouts/Root/index.tsx

@@ -5,11 +5,10 @@ import { rtlLanguages } from '@payloadcms/translations'
 import { RootProvider } from '@payloadcms/ui'
 import { getClientConfig } from '@payloadcms/ui/utilities/getClientConfig'
 import { headers as getHeaders, cookies as nextCookies } from 'next/headers.js'
-import { getPayload, parseCookies } from 'payload'
+import { getPayload, getRequestLanguage, parseCookies } from 'payload'
 import React from 'react'
 
 import { getNavPrefs } from '../../elements/Nav/getNavPrefs.js'
-import { getRequestLanguage } from '../../utilities/getRequestLanguage.js'
 import { getRequestLocale } from '../../utilities/getRequestLocale.js'
 import { getRequestTheme } from '../../utilities/getRequestTheme.js'
 import { initReq } from '../../utilities/initReq.js'

packages/next/src/routes/graphql/handler.ts

@@ -4,13 +4,14 @@ import type { APIError, Payload, PayloadRequest, SanitizedConfig } from 'payload
 import { configToSchema } from '@payloadcms/graphql'
 import { createHandler } from 'graphql-http/lib/use/fetch'
 import httpStatus from 'http-status'
-import { logError } from 'payload'
-
-import { addDataAndFileToRequest } from '../../utilities/addDataAndFileToRequest.js'
-import { addLocalesToRequestFromData } from '../../utilities/addLocalesToRequest.js'
-import { createPayloadRequest } from '../../utilities/createPayloadRequest.js'
-import { headersWithCors } from '../../utilities/headersWithCors.js'
-import { mergeHeaders } from '../../utilities/mergeHeaders.js'
+import {
+  addDataAndFileToRequest,
+  addLocalesToRequestFromData,
+  createPayloadRequest,
+  headersWithCors,
+  logError,
+  mergeHeaders,
+} from 'payload'
 
 const handleError = async ({
   err,

packages/next/src/routes/graphql/playground.ts

@@ -1,8 +1,5 @@
-import type { SanitizedConfig } from 'payload'
-
 import { renderPlaygroundPage } from 'graphql-playground-html'
-
-import { createPayloadRequest } from '../../utilities/createPayloadRequest.js'
+import { createPayloadRequest, type SanitizedConfig } from 'payload'
 
 export const GET = (config: Promise<SanitizedConfig>) => async (request: Request) => {
   const req = await createPayloadRequest({