metal: implement VRR

src/it/test_backend.rs

@@ -110,6 +110,7 @@ impl TestBackend {
             width_mm: 80,
             height_mm: 60,
             non_desktop: false,
+            vrr_capable: false,
         };
         Self {
             state: state.clone(),

src/it/tests/t0034_workspace_restoration.rs

@@ -43,6 +43,7 @@ async fn test(run: Rc<TestRun>) -> TestResult {
         width_mm: 0,
         height_mm: 0,
         non_desktop: false,
+        vrr_capable: false,
     };
     run.backend
         .state