Fix the Plastik decoration with Qt 5.15

The trick in qmldir no longer works with Qt 5.15, so use a more reliable
approach. This way works with Qt 5.15 and also on previous versions of Qt.

plugins/kdecorations/aurorae/themes/plastik/code/plastikplugin.cpp

@@ -20,7 +20,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 void PlastikPlugin::registerTypes(const char *uri)
 {
-    Q_UNUSED(uri)
+    // Need to register something to tell Qt that it loaded (QTBUG-84571)
+    qmlRegisterModule(uri, 1, 0);
 }
 
 void PlastikPlugin::initializeEngine(QQmlEngine *engine, const char *uri)

plugins/kdecorations/aurorae/themes/plastik/code/qmldir

@@ -1,5 +1,2 @@
 module org.kde.kwin.decorations.plastik
 plugin plastikplugin
-
-# we need to have at least one element of Qt is not able to find the plugin *shrug*
-Foo 1.0 Foo.qml