qmlscene calls QApplication::installTranslator() without QT_WIDGETS_LIB guards

In the method loadTranslationFile() of qtdeclarative/tools/qmlscene/main.cpp, qmlscene makes a reference to QApplication, despite being written elsewhere to support both widget- and non-widget builds. This prevents qmlscene from building if the QtWidgets module is unavailable.

Switching to QCoreApplication::installTranslator() should be a sufficient fix.