mash: Rename browser_driver to app_driver.

mash/app_driver/manifest.json

 {
   "manifest_version":  1,
-  "name": "mojo:browser_driver",
-  "display_name": "Browser Driver",
+  "name": "mojo:app_driver",
+  "display_name": "App Driver",
   "capabilities": {
     "required": {
       "*": {
         "classes": [ "mus:window_manager" ]
       },
       "exe:chrome": {
         "classes": [ "mash:launchable" ]
       },
       "mojo:catalog": {
         "interfaces": [ "catalog::mojom::Catalog" ]
       }
     }
   }
 }