preview should emit fileLoaded

with that signal we can remove language changed workaround

• qmlpreviewconnectionmanager.cpp

  //emitlanguageafterafilewasloadedanddoiteverytime,
  //becausethisalsotriggersthecheckformissingtranslations
  emit language(m_lastUsedLanguage);
  

• qmldebugtranslationrunner

   //changing file causes languageChanged signal to trigger, we don't want to handle it now!
              QObject::disconnect(debugTranslationClient, &AdvancedQmlDebugTranslationClient::languageChanged,
                                  this, nullptr);
  ...
              QTimer::singleShot(2000, debugTranslationClient, [this]() {
                  emit q->progressed();
                  debugTranslationClient->getStateList();
              });