Draft: Edit, change startEditing method to accept (obj, node_idx)

This enable to start editing also without an user click event, by just calling the method and specifying the object and the edit point index.
It is used for alternative edit mode (alt_edit_mode) by arc context menu

src/Mod/Draft/draftguitools/gui_edit.py

@@ -457,7 +457,16 @@ class Edit(gui_base_original.Modifier):
             ):#left click
             if not event.wasAltDown():
                 if self.editing is None:
-                    self.startEditing(event)
+
+                    pos = event.getPosition()
+                    node = self.getEditNode(pos)
+                    node_idx = self.getEditNodeIndex(node)
+                    if node_idx is None:
+                        return
+                    doc = App.getDocument(str(node.documentName.getValue()))
+                    obj = doc.getObject(str(node.objectName.getValue()))
+
+                    self.startEditing(obj, node_idx)
                 else:
                     self.endEditing(self.obj, self.editing)
             elif event.wasAltDown():  # left click with ctrl down
@@ -486,32 +495,25 @@ class Edit(gui_base_original.Modifier):
                     self.overNode.setColor(COLORS["default"])
                     self.overNode = None
 
-    def startEditing(self, event):
+    def startEditing(self, obj, node_idx):
         """Start editing selected EditNode."""
-        pos = event.getPosition()
-        node = self.getEditNode(pos)
-        ep = self.getEditNodeIndex(node)
-        if ep is None:
+        self.obj = obj # this is still needed to handle preview
+        if obj is None:
             return
 
-        doc = App.getDocument(str(node.documentName.getValue()))
-        self.obj = doc.getObject(str(node.objectName.getValue()))
-        if self.obj is None:
-            return
-
-        App.Console.PrintMessage(self.obj.Name
+        App.Console.PrintMessage(obj.Name
                                  + ": editing node number "
-                                 + str(ep) + "\n")
+                                 + str(node_idx) + "\n")
 
         self.ui.lineUi()
         self.ui.isRelative.show()
-        self.editing = ep
-        self.trackers[self.obj.Name][self.editing].off()
+        self.editing = node_idx
+        self.trackers[obj.Name][node_idx].off()
 
         self.finalizeGhost()
-        self.initGhost(self.obj)
+        self.initGhost(obj)
 
-        self.node.append(self.trackers[self.obj.Name][self.editing].get())
+        self.node.append(self.trackers[obj.Name][node_idx].get())
         Gui.Snapper.setSelectMode(False)
         self.hideTrackers()
 

src/Mod/Draft/draftguitools/gui_edit_draft_objects.py

@@ -290,7 +290,7 @@ class DraftCircleGuiTools(GuiTools):
         if action in ("move arc", "set radius",
                 "set first angle", "set last angle"):
             edit_command.alt_edit_mode = 1
-            edit_command.startEditing(edit_command.event)
+            edit_command.startEditing(obj, node_idx)
 
     def init_preview_object(self, obj):
         return trackers.arcTracker()