[BUGFIX] Fix FormEngine inline stylesheet resolution in composer mode

The public URL resolution in lazy loaded TCA forms (e.g. inline records)
is aligned to use the same path resolution mechanism as in PageRender.

Releases: main, 12.4, 11.5
Resolves: #103296
Change-Id: I981af29b34393302c49dd16216f0baa580d60767
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83399


Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>

typo3/sysext/backend/Classes/Controller/AbstractFormEngineAjaxController.php

@@ -18,6 +18,7 @@ declare(strict_types=1);
 namespace TYPO3\CMS\Backend\Controller;
 
 use TYPO3\CMS\Backend\Form\FormResultTrait;
+use TYPO3\CMS\Core\Core\Environment;
 use TYPO3\CMS\Core\Localization\LanguageService;
 use TYPO3\CMS\Core\Localization\LocalizationFactory;
 use TYPO3\CMS\Core\Page\JavaScriptItems;
@@ -106,7 +107,8 @@ abstract class AbstractFormEngineAjaxController
     protected function getRelativePathToStylesheetFile(string $stylesheetFile): string
     {
         if (PathUtility::isExtensionPath($stylesheetFile)) {
-            $stylesheetFile = GeneralUtility::getFileAbsFileName($stylesheetFile);
+            // @see PageRenderer::getStreamlinedFileName()
+            $stylesheetFile = Environment::getPublicPath() . '/' . PathUtility::getPublicResourceWebPath($stylesheetFile, false);
             $stylesheetFile = PathUtility::getRelativePathTo($stylesheetFile) ?? '';
             $stylesheetFile = rtrim($stylesheetFile, '/');
         } else {