plugins/desktopchangeosd: Port to simpler PlasmaWindow

Plasma::Dialog contains logic that we don't want for a kwin window and
is considered deprecated. Dialog uses the width of the main item which
results in an unavoidable binding loop.

PlasmaWindow allows us to propagate implicit sizes upwards correctly.

BUG: 420757

src/plugins/desktopchangeosd/package/contents/ui/osd.qml

@@ -13,12 +13,13 @@ import org.kde.kirigami 2.20 as Kirigami
 import org.kde.ksvg 1.0 as KSvg
 import org.kde.kwin
 
-PlasmaCore.Dialog {
+PlasmaCore.Window {
     id: dialog
-    location: PlasmaCore.Types.Floating
     visible: false
     flags: Qt.X11BypassWindowManagerHint | Qt.FramelessWindowHint
-    outputOnly: true
+
+    width: mainItem.implicitWidth + leftPadding + rightPadding
+    height: mainItem.implicitHeight + topPadding + bottomPadding
 
     mainItem: Item {
         function loadConfig() {
@@ -38,8 +39,8 @@ PlasmaCore.Dialog {
         property int animationDuration: 1000
         property bool showGrid: true
 
-        width: dialogItem.showGrid ? view.itemWidth * view.columns : Math.ceil(textElement.implicitWidth)
-        height: dialogItem.showGrid ? view.itemHeight * view.rows + textElement.height : textElement.height
+        implicitWidth: dialogItem.showGrid ? view.itemWidth * view.columns : Math.ceil(textElement.implicitWidth)
+        implicitHeight: dialogItem.showGrid ? view.itemHeight * view.rows + textElement.implicitHeight : textElement.implicitHeight
 
         Kirigami.Heading {
             id: textElement