plugins/overview: Adds a border around hovered and selected desktop in desktopGrid

Currently desktop grid view is missing the selection rectangle when hovered over a desktop.
This adds the selection rectangle on hover, since it used to be there before three-state design.

Currently selected desktop has thinner and different colored border.


![image](/uploads/ad1f2f7acbe602fb7b9479ce859026b7/image.png)

![image](/uploads/9fa50bac4b81958da0b8926f8d2518ba/image.png)

![image](/uploads/3e46c1f5a740c40bbf18a5d887f31d39/image.png)

BUG:481812

src/plugins/overview/qml/main.qml

@@ -524,7 +524,7 @@ FocusScope {
                     Kirigami.ShadowedTexture {
                         anchors.fill: parent
 
-                        color: Kirigami.Theme.highlightColor
+                        color: "transparent"
                         source: desktopElement
 
                         radius: Kirigami.Units.largeSpacing * 2 * (overviewVal + gridVal * 2)
@@ -534,6 +534,11 @@ FocusScope {
                             color: Qt.rgba(0, 0, 0, 0.3)
                             yOffset: 3
                         }
+
+                        property var borderWidth: desktopHover.hovered ? Kirigami.Units.largeSpacing : (mainBackground.current ? Kirigami.Units.smallSpacing : 0);
+                        property var borderColor: desktopHover.hovered ? Kirigami.Theme.focusColor : (mainBackground.current ? Kirigami.Theme.highlightColor : "transparent")
+                        border.width: gridVal == 1 ? borderWidth : 0
+                        border.color: gridVal == 1 ? borderColor : "transparent"
                     }
 
                     DropArea {
@@ -593,6 +598,10 @@ FocusScope {
                             }
                         }
                     }
+
+                    HoverHandler {
+                        id: desktopHover
+                    }
                 }
 
                 WindowHeap {