output_configuration: Set wlr_output_head serial number

src/backend/kms/device.rs

@@ -949,6 +949,10 @@ fn create_output_for_conn(drm: &mut DrmDevice, conn: connector::Handle) -> Resul
                 .as_ref()
                 .and_then(|info| info.model())
                 .unwrap_or_else(|| String::from("Unknown")),
+            serial_number: edid_info
+                .as_ref()
+                .and_then(|info| info.serial())
+                .unwrap_or_else(|| String::from("Unknown")),
         },
     );
     if let Some(edid) = edid_info.as_ref().and_then(|x| x.edid()) {

src/backend/winit.rs

@@ -148,6 +148,7 @@ pub fn init_backend(
         subpixel: Subpixel::Unknown,
         make: "COSMIC".to_string(),
         model: name.clone(),
+        serial_number: "Unknown".to_string(),
     };
     let mode = Mode {
         size: (size.w, size.h).into(),

src/backend/x11.rs

@@ -94,6 +94,7 @@ impl X11State {
             subpixel: Subpixel::Unknown,
             make: "COSMIC".to_string(),
             model: name.clone(),
+            serial_number: "Unknown".to_string(),
         };
         let mode = Mode {
             size: (size.w as i32, size.h as i32).into(),

src/wayland/protocols/output_configuration/mod.rs

@@ -507,6 +507,9 @@ where
         if physical.model != "Unknown" {
             instance.obj.model(physical.model);
         }
+        if physical.serial_number != "Unknown" {
+            instance.obj.serial_number(physical.serial_number);
+        }
     }
 
     if let Some(extension_obj) = instance.extension_obj.as_ref() {