RT state managment and rectangle support

dotnet/AipsRT/Model/Whiteboard/Shapes/Line.cs

@@ -0,0 +1,10 @@
+using AipsRT.Model.Whiteboard.Structs;
+
+namespace AipsRT.Model.Whiteboard.Shapes;
+
+public class Line : Shape
+{
+    public Position EndPosition { get; set; }
+    
+    public int Thickness { get; set; }
+}