backend: make input device properties readable

src/backend.rs

@@ -118,14 +118,38 @@ pub trait InputDevice {
     fn on_change(&self, cb: Rc<dyn Fn()>);
     fn grab(&self, grab: bool);
     fn has_capability(&self, cap: InputDeviceCapability) -> bool;
+    fn left_handed(&self) -> Option<bool> {
+        None
+    }
     fn set_left_handed(&self, left_handed: bool);
+    fn accel_profile(&self) -> Option<InputDeviceAccelProfile> {
+        None
+    }
     fn set_accel_profile(&self, profile: InputDeviceAccelProfile);
+    fn accel_speed(&self) -> Option<f64> {
+        None
+    }
     fn set_accel_speed(&self, speed: f64);
+    fn transform_matrix(&self) -> Option<TransformMatrix> {
+        None
+    }
     fn set_transform_matrix(&self, matrix: TransformMatrix);
     fn name(&self) -> Rc<String>;
+    fn tap_enabled(&self) -> Option<bool> {
+        None
+    }
     fn set_tap_enabled(&self, enabled: bool);
+    fn drag_enabled(&self) -> Option<bool> {
+        None
+    }
     fn set_drag_enabled(&self, enabled: bool);
+    fn drag_lock_enabled(&self) -> Option<bool> {
+        None
+    }
     fn set_drag_lock_enabled(&self, enabled: bool);
+    fn natural_scrolling_enabled(&self) -> Option<bool> {
+        None
+    }
     fn set_natural_scrolling_enabled(&self, enabled: bool);
 }