支持画笔及痕迹擦除，为白板做准备

AIStudio.Wpf.DiagramDesigner/Enums/DrawMode.cs

@@ -6,17 +6,26 @@ namespace AIStudio.Wpf.DiagramDesigner
 {
     public enum DrawMode
     {
-        Normal = 0,
-        Line = 1,
-        Rectangle = 2,
-        Ellipse = 3,
-        Polyline = 4,
-        Polygon = 5,
-        DirectLine = 6,
+        Normal = 0,       
         ConnectingLineSmooth = 10,
         ConnectingLineStraight = 11,
         ConnectingLineCorner = 12,
-        ConnectingLineBoundary = 13,        
-        Text = 20,
+        ConnectingLineBoundary = 13,
+        //101-110为可部分擦除的形状
+        Eraser = 100,
+        Line = 101,
+        Rectangle = 102,
+        Ellipse = 103,
+        Polyline = 104,
+        Polygon = 105,
+        DirectLine = 106,
+        //不可部分擦除
+        FillableLine = 111,
+        FillableRectangle = 112,
+        FillableEllipse = 113,
+        FillablePolyline = 114,
+        FillablePolygon = 115,
+        FillableDirectLine = 116,
+        Text = 200,
     }
 }