Renames mojo:desktop_wm to mojo:ash

mash/unittests_manifest.json

 {
   "manifest_version":  1,
   "name": "exe:mash_unittests",
   "display_name": "Mash Unittests",
   "capabilities": {
     "required": {
       "*": { "classes": [ "app", "test" ] },
-      "mojo:desktop_wm": {
+      "mojo:ash": {
         "interfaces": [
           "mus::mojom::AcceleratorRegistrar",
           "ash::mojom::UserWindowController"
         ]
       }
     }
   }
 }