Quick Controls 2 plugin does not load statically built custom style plugins when using dynamically built Qt.

This suggestion is related to https://bugreports.qt.io/browse/QTBUG-67062

According to the change request https://codereview.qt-project.org/#/c/229114/11/src/imports/controls/qtquickcontrols2plugin.cpp static plugins are only loaded and initialised when using static Qt build, so the suggestion is to load also static style plugins even when using dynamically built Qt.