system tray: allow re-ordering tray items

quickshell/Common/SessionData.qml

@@ -95,6 +95,7 @@ Singleton {
     property var barPinnedApps: []
     property int dockLauncherPosition: 0
     property var hiddenTrayIds: []
+    property var trayItemOrder: []
     property var recentColors: []
     property bool showThirdPartyPlugins: false
     property string launchPrefix: ""
@@ -871,6 +872,11 @@ Singleton {
         return trayId && hiddenTrayIds.indexOf(trayId) !== -1;
     }
 
+    function setTrayItemOrder(order) {
+        trayItemOrder = order;
+        saveSettings();
+    }
+
     function addRecentColor(color) {
         const colorStr = color.toString();
         let recent = recentColors.slice();

quickshell/Common/settings/SessionSpec.js

@@ -50,6 +50,7 @@ var SPEC = {
     barPinnedApps: { def: [] },
     dockLauncherPosition: { def: 0 },
     hiddenTrayIds: { def: [] },
+    trayItemOrder: { def: [] },
     recentColors: { def: [] },
     showThirdPartyPlugins: { def: false },
     launchPrefix: { def: "" },