feat(cursor): carry the remote bitmap pixel density

libs/base/protos/message.proto

@@ -316,6 +316,8 @@ message CursorData {
   int32 width = 4;
   int32 height = 5;
   bytes colors = 6;
+  // Physical bitmap pixels per remote logical pixel; 0 means an older sender.
+  double scale = 7;
 }
 
 message CursorPosition {

src/flutter.rs

@@ -651,6 +651,7 @@ impl InvokeUiSession for FlutterHandler {
                 ("hoty", &cd.hoty.to_string()),
                 ("width", &cd.width.to_string()),
                 ("height", &cd.height.to_string()),
+                ("scale", &cd.scale.to_string()),
                 (
                     "colors",
                     &serde_json::ser::to_string(&colors).unwrap_or("".to_owned()),