Add missing SiXml import

- Add SiXml to import list to fix ReferenceError
- SiXml was being used in iconMap but not imported
- All XML files now properly display XML icon

src/ui/Desktop/Apps/File Manager/components/FileViewer.tsx

@@ -34,6 +34,7 @@ import {
   SiSass,
   SiLess,
   SiJson,
+  SiXml,
   SiYaml,
   SiToml,
   SiShell,