Support svgz buttons in Aurorae themes

The Aurorae decoration engine in KWin checks for svgz icons if the svg
does not exist. Do the same thing here.

BUG: 432712


(cherry picked from commit 0bea4e6e)

kded/kwin_bridge/auroraedecorationpainter.cpp

@@ -25,7 +25,10 @@ void AuroraeDecorationPainter::paintButton(QPainter &painter, const QString &but
     const QString buttonFileName = buttonTypeToFileName(buttonType);
     const QString elementIdName = buttonStateToElementId(buttonState);
 
-    QSvgRenderer buttonRenderer {m_themePath + buttonFileName};
+    const QString buttonFilePath = m_themePath + buttonFileName;
+
+    QSvgRenderer buttonRenderer;
+    buttonRenderer.load(buttonFilePath) || buttonRenderer.load(buttonFilePath + "z");
     buttonRenderer.render(&painter, elementIdName, DecorationPainter::ButtonGeometry);
 }