Move TestDisplayController into own capability class.

services/ui/manifest.json

 {
   "name": "ui",
   "display_name": "UI Service",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         // A collection of interfaces needed by a generic client of mus.
         // Additional interfaces may be requested a-la-carte.
         // NOTE: when adding a new interface chances are you will want to add it
         // to window_manager as well.
@@ skipping 10 matching lines @@
         // Interfaces provided by mus-gpu for mus-ws.
         "ozone": [
           "ui::ozone::mojom::DeviceCursor"
         ],
         "test": [
           "ui::mojom::WindowServerTest"
         ],
         "discardable_memory": [
           "discardable_memory::mojom::DiscardableSharedMemoryManager"
         ],
+        "display_test": [
+          "display::mojom::TestDisplayController"
+        ],
         "gpu_client": [
           "ui::mojom::Gpu"
         ],
         "ime_registrar": [
           "ui::mojom::IMERegistrar"
         ],
         "user_access_manager": [
           "ui::mojom::UserAccessManager"
         ],
         "window_manager": [
           "discardable_memory::mojom::DiscardableSharedMemoryManager",
           "display::mojom::DisplayController",
-          "display::mojom::TestDisplayController",
           "ui::mojom::AccessibilityManager",
           "ui::mojom::Clipboard",
           "ui::mojom::DisplayCompositor",
           "ui::mojom::DisplayManager",
           "ui::mojom::Gpu",
           "ui::mojom::IMEServer",
           "ui::mojom::InputDeviceServer",
           "ui::mojom::UserActivityMonitor",
           "ui::mojom::WindowManagerWindowTreeFactory"
         ],
         "window_tree_host_factory": [
           "ui::mojom::WindowTreeHostFactory"
         ]
       },
       "requires": {
         "*": [ "app" ],
         "catalog": [ "app" ],
         "service_manager": [ "service_manager:all_users" ],
         "ui": [ "ozone" ]
       }
     }
   }
 }