bug #4001 Do not drop specific css class on transform field (zorn-v)

This PR was squashed before being merged into the 3.0.x-dev branch.

Discussion
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Do not drop specific css class on transform field

Fixes #3997

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Commits
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94b682b Do not drop specific css class on transform field

src/Factory/FieldFactory.php

@@ -145,7 +145,7 @@ private function transformField(FieldDto $fieldDto, string $newFieldFqcn): Field
         $newField->setDisplayedOn($fieldDto->getDisplayedOn());
         $newField->setValue($fieldDto->getValue());
         $newField->setFormattedValue($fieldDto->getFormattedValue());
-        $newField->setCssClass($fieldDto->getCssClass());
+        $newField->setCssClass(trim($newField->getCssClass().' '.$fieldDto->getCssClass()));
         $newField->setTranslationParameters($fieldDto->getTranslationParameters());
         $newField->setAssets($newField->getAssets()->mergeWith($fieldDto->getAssets()));