Restore EditorLinkDialog form and add link text field support for Drupal 11

Problem/Motivation

When attempting to open the link dialog using CKEditor 4 in Drupal 11, the editor triggers an AJAX 404 error:

An AJAX HTTP error occurred.
HTTP Result Code: 404
Path: /editor/dialog/link/basic_html
ResponseText: {"message":"No route found for \"POST https://example.com/editor/dialog/link/basic_html\""}

In Drupal 8/9/10, EditorLinkDialog.php and the associated route /editor/dialog/link/{editor} were hosted in Drupal core's editor module. When CKEditor 4 core integration was removed in Drupal 10/11, that controller and route were dropped from core.

Steps to reproduce

1. Install Drupal 11 with the ckeditor (CKEditor 4) contrib module.
2. Edit a text format (e.g., Basic HTML) to use CKEditor 4.
3. Edit a node using this text format and click the Link icon in the CKEditor toolbar.
4. Result: Browser console reports a 404 AjaxError on /editor/dialog/link/basic_html.

Proposed resolution

Move EditorLinkDialog.php from legacy core paths into modules/contrib/ckeditor/src/Form/EditorLinkDialog.php.
Registers the route /editor/dialog/link/{editor} mapping to EditorLinkDialog in ckeditor.routing.yml .