Fix: missing system logo and app icons on Guix System (#616)

* Fix for Guix logo not being shown

* Fixed icons not being shown in Workspace Switcher. Also added a DesktopService with a function to get the icon path

* Fixed some icons not being shown + Icons in app drawer

* Fixed icons not appearing in Spotlight

* Adapted missing icons in app launcher/spotlight

* Removed (now) useless change

Services/DesktopService.qml

@@ -0,0 +1,63 @@
+pragma Singleton
+
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import Quickshell
+import Quickshell.Io
+
+Singleton {
+    id: root
+    function resolveIconPath(moddedAppId) {
+    	     const entry = DesktopEntries.heuristicLookup(moddedAppId)
+    	     const appIds = [moddedAppId, moddedAppId.toLowerCase()];
+
+    	     const lastPart = moddedAppId.split('.').pop();
+    	     if (lastPart && lastPart !== moddedAppId) {
+                  appIds.push(lastPart);
+
+        	  const firstChar = lastPart.charAt(0);
+        	  const rest = lastPart.slice(1);
+        	  let toggled;
+
+        	  if (firstChar === firstChar.toLowerCase()) {
+            	     toggled = firstChar.toUpperCase() + rest;
+        	  } else {
+            	     toggled = firstChar.toLowerCase() + rest;
+        	  }
+
+        	  if (toggled !== lastPart) {
+            	     appIds.push(toggled);
+        	  }
+    	     }
+	     for (const appId of appIds){
+    	     let icon = Quickshell.iconPath(entry?.icon, true)
+	     console.log(icon)
+    	     if (icon && icon !== "") return icon
+
+    	     let execPath = entry?.execString?.replace(/\/bin.*/, "")
+	     console.log(execPath)
+    	     if (!execPath) continue
+
+	     //Check that the app is installed with nix/guix
+    	     if (execPath.startsWith("/nix/store/") || execPath.startsWith("/gnu/store/")) {
+             const basePath = execPath
+             const sizes = ["256x256", "128x128", "64x64", "48x48", "32x32", "24x24", "16x16"]
+
+	     let iconPath = `${basePath}/share/icons/hicolor/scalable/apps/${appId}.svg`
+            	 icon = Quickshell.iconPath(iconPath, true)
+		 console.log(icon)
+		 if (icon && icon !== "") return icon
+
+             for (const size of sizes) {
+             	 iconPath = `${basePath}/share/icons/hicolor/${size}/apps/${appId}.png`
+            	 icon = Quickshell.iconPath(iconPath, true)
+		 console.log(icon)
+		 if (icon && icon !== "") return icon
+       	     }
+	     }
+    }
+
+    return ""
+}
+}