Use ThickMargin to redirect mouse input to panel and update spacingAtMinSize value

(cherry picked from commit c540181a)

desktoppackage/contents/views/Panel.qml

@@ -35,11 +35,17 @@ PlasmaCore.FrameSvgItem {
 
     readonly property bool verticalPanel: containment && containment.formFactor === PlasmaCore.Types.Vertical
 
-    readonly property real spacingAtMinSize: Math.max(1, (verticalPanel ? root.width : root.height) - PlasmaCore.Units.iconSizes.smallMedium - PlasmaCore.Units.smallSpacing*2)/2
-    readonly property int topPadding: Math.round(Math.min(root.fixedMargins.top, spacingAtMinSize));
-    readonly property int bottomPadding: Math.round(Math.min(root.fixedMargins.bottom, spacingAtMinSize));
-    readonly property int leftPadding: Math.round(Math.min(root.fixedMargins.left, spacingAtMinSize));
-    readonly property int rightPadding: Math.round(Math.min(root.fixedMargins.right, spacingAtMinSize));
+    readonly property real spacingAtMinSize: Math.round(Math.max(1, (verticalPanel ? root.width : root.height) - units.iconSizes.smallMedium)/2)
+    PlasmaCore.FrameSvgItem {
+        id: thickPanelSvg
+        visible: false
+        prefix: 'thick'
+        imagePath: "widgets/panel-background"
+    }
+    readonly property int topPadding: Math.round(Math.min(thickPanelSvg.fixedMargins.top, spacingAtMinSize));
+    readonly property int bottomPadding: Math.round(Math.min(thickPanelSvg.fixedMargins.bottom, spacingAtMinSize));
+    readonly property int leftPadding: Math.round(Math.min(thickPanelSvg.fixedMargins.left, spacingAtMinSize));
+    readonly property int rightPadding: Math.round(Math.min(thickPanelSvg.fixedMargins.right, spacingAtMinSize));
 
     function adjustPrefix() {
         if (!containment) {