feat!: auto-removes localized property from localized fields within other localized fields (#7933)

## Description

Payload localization works on a field-by-field basis. As you can nest
fields within other fields, you could potentially nest a localized field
within a localized field—but this would be redundant and unnecessary.
There would be no reason to define a localized field within a localized
parent field, given that the entire data structure from the parent field
onward would be localized.

Up until this point, Payload would _allow_ you to nest a localized field
within another localized field, and this might have worked in MongoDB
but it will throw errors in Postgres.

Now, Payload will automatically remove the `localized: true` property
from sub-fields within `sanitizeFields` if a parent field is localized.

This could potentially be a breaking change if you have a configuration
with MongoDB that nests localized fields within localized fields.

## Migrating

You probably only need to migrate if you are using MongoDB, as there,
you may not have noticed any problems. But in Postgres or SQLite, this
would have caused issues so it's unlikely that you've made it too far
without experiencing issues due to a nested localized fields config.

In the event you would like to keep existing data in this fashion, we
have added a `compatibility.allowLocalizedWithinLocalized` flag to the
Payload config, which you can set to `true`, and Payload will then
disable this new sanitization step.

Set this compatibility flag to `true` only if you have an existing
Payload MongoDB database from pre-3.0, and you have nested localized
fields that you would like to maintain without migrating.

test/localization/int.spec.ts

@@ -6,7 +6,6 @@ import { fileURLToPath } from 'url'
 import type { NextRESTClient } from '../helpers/NextRESTClient.js'
 import type { LocalizedPost, WithLocalizedRelationship } from './payload-types.js'
 
-import { englishLocale } from '../globals/config.js'
 import { idToString } from '../helpers/idToString.js'
 import { initPayloadInt } from '../helpers/initPayloadInt.js'
 import { arrayCollectionSlug } from './collections/Array/index.js'
@@ -15,6 +14,7 @@ import { nestedToArrayAndBlockCollectionSlug } from './collections/NestedToArray
 import { tabSlug } from './collections/Tab/index.js'
 import {
   defaultLocale,
+  defaultLocale as englishLocale,
   englishTitle,
   hungarianLocale,
   localizedPostsSlug,
@@ -1396,6 +1396,17 @@ describe('Localization', () => {
     })
   })
 
+  describe('nested localized field sanitization', () => {
+    it('should sanitize nested localized fields', () => {
+      const collection = payload.collections['localized-within-localized'].config
+
+      expect(collection.fields[0].tabs[0].fields[0].localized).toBeUndefined()
+      expect(collection.fields[1].fields[0].localized).toBeUndefined()
+      expect(collection.fields[2].blocks[0].fields[0].localized).toBeUndefined()
+      expect(collection.fields[3].fields[0].localized).toBeUndefined()
+    })
+  })
+  
   describe('nested blocks', () => {
     let id
     it('should allow creating nested blocks per locale', async () => {