[TASK] Use ckeditor's native readOnly mode

Textarea can be configured in TCA to be read only and to have a richtext
editor enabled. If `readOnly` is enabled, ckeditor is now rendered in a
read-only mode instead of rendering a plain textarea containing HTML
markup.

Resolves: #97296
Releases: main, 11.5
Change-Id: I9e457123811ef53ad4e3e355a68e3f1e5701dcfc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74180


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>

typo3/sysext/rte_ckeditor/Classes/Form/Element/RichTextElement.php

@@ -346,6 +346,10 @@ class RichTextElement extends AbstractFormElement
             'customConfig' => '',
         ];
 
+        if ($this->data['parameterArray']['fieldConf']['config']['readOnly'] ?? false) {
+            $configuration['readOnly'] = true;
+        }
+
         if (is_array($this->rteConfiguration['config'] ?? null)) {
             $configuration = array_replace_recursive($configuration, $this->rteConfiguration['config']);
         }

typo3/sysext/rte_ckeditor/Classes/Form/Resolver/RichTextNodeResolver.php

@@ -53,10 +53,8 @@ class RichTextNodeResolver implements NodeResolverInterface
     {
         $parameterArray = $this->data['parameterArray'];
         $backendUser = $this->getBackendUserAuthentication();
-        if (// This field is not read only
-            !($parameterArray['fieldConf']['config']['readOnly'] ?? false)
-            // If RTE is generally enabled by user settings and RTE object registry can return something valid
-            && $backendUser->isRTE()
+        if (// If RTE is generally enabled by user settings and RTE object registry can return something valid
+            $backendUser->isRTE()
             // If RTE is enabled for field
             && (bool)($parameterArray['fieldConf']['config']['enableRichtext'] ?? false) === true
             // If RTE config is found (prepared by TcaText data provider)