Add import of polygon from dxf

StructureHelperCommon/Models/Shapes/Logics/IArcFlatteningOption.cs

@@ -0,0 +1,10 @@
+namespace StructureHelperCommon.Models.Shapes
+{
+    public interface IArcFlatteningOption
+    {
+        double AngleStepRadians { get; set; }
+        double MaxSegmentLength { get; set; }
+        ArcFlatteningMode Mode { get; set; }
+        int SegmentCount { get; set; }
+    }
+}