♻️ Use already existing asset collector

For some reason the AssetCollector instance created (or passed) in the
PageRendererPreProcess constructor was not used, but instead a new
instance was made as part of the addLibrary function.

This commit refactors PageRendererPreProcess::addLibrary to use the
already created AssetCollector.

Classes/Hooks/PageRendererPreProcess.php

@@ -29,8 +29,7 @@ class PageRendererPreProcess
         $plausible = $this->getPlausibleURL();
 
         if (isset($domain) && isset($plausible) && !$this->tsfe->isBackendUserLoggedIn()) {
-            GeneralUtility::makeInstance(AssetCollector::class)
-                ->addJavaScript(
+            $this->assetCollector->addJavaScript(
                 'plausible_analytics',
                 $plausible . '/js/plausible.js',
                 [