perf(richtext-lexical): do not return i18n from editor adapter (#14228)

This PR deprecates the `i18n` property returned from the editor adapter.
Instead, we now merge `i18n` directly into the `config`, since the
config is already available in the richtext adapter provider. This
simplifies the logic (only one line of code) and eliminates the need to
manually read and merge i18n from the adapter.

Benefits:
- **Simpler implementation**: Merging i18n into the config is
straightforward
- **Reduced memory usage**: Each editor no longer maintains its own i18n
object - only a single, merged `config.i18n` is kept.
- **Improved developer experience**: The sanitized field config is now
smaller and easier to inspect. Console logging the config no longer
floods the output with hundreds of translation lines.

---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1211668727538425

Author: AlessioGr

packages/payload/src/admin/RichText.ts

@@ -235,6 +235,10 @@ type RichTextAdapterBase<
     siblingDoc: JsonObject
   }) => void
   hooks?: RichTextHooks
+  /**
+   * @deprecated - manually merge i18n translations into the config.i18n.translations object within the adapter provider instead.
+   * This property will be removed in v4.
+   */
   i18n?: Partial<GenericLanguages>
   outputSchema?: (args: {
     collectionIDFieldTypes: { [key: string]: 'number' | 'string' }

packages/richtext-lexical/src/index.ts

@@ -7,6 +7,7 @@ import {
   beforeChangeTraverseFields,
   beforeValidateTraverseFields,
   checkDependencies,
+  deepMergeSimple,
   withNullableJSONSchemaType,
 } from 'payload'
 
@@ -93,6 +94,8 @@ export function lexicalEditor(args?: LexicalEditorProps): LexicalRichTextAdapter
       featureI18n[lang].lexical.general = i18n[lang]
     }
 
+    config.i18n.translations = deepMergeSimple(config.i18n.translations, featureI18n)
+
     return {
       CellComponent: {
         path: '@payloadcms/richtext-lexical/rsc#RscEntryLexicalCell',
@@ -783,7 +786,6 @@ export function lexicalEditor(args?: LexicalEditorProps): LexicalRichTextAdapter
           },
         ],
       },
-      i18n: featureI18n,
       outputSchema: ({
         collectionIDFieldTypes,
         config,