Render rotated plasmoids via off screen framebuffer

When rotated most applets, especially text look garbage.

If we render into an offscreen buffer we can smooth things out and it
looks good again. There is a performance penalty to this, but most
people do no not rotate plasmoids.

components/containmentlayoutmanager/qml/BasicAppletContainer.qml

@@ -88,6 +88,11 @@ ContainmentLayoutManager.AppletContainer {
     rightPadding: background.margins.right
     bottomPadding: background.margins.bottom
 
+    // render via a layer if we're at an angle
+    // resize handles are rendered outside this item, so also disable when they're showing to avoid clipping
+    layer.enabled: (rotation % 90 != 0) && !(configOverlayItem && configOverlayItem.visible)
+    layer.smooth: true
+
     initialSize.width: applet.switchWidth + leftPadding + rightPadding
     initialSize.height: applet.switchHeight + topPadding + bottomPadding