Draft: move arc_3points to the make package

Also import it in the `Draft` namespace so that is available
as `Draft.make_arc_3points`.

Use this new function in the unit test `drafttests.test_creation`,
in the GuiCommand `draftguitools.gui_arcs`, and in the
`draft_test_objects` script.

src/Mod/Draft/drafttests/draft_test_objects.py

@@ -32,11 +32,11 @@ Or load it as a module and use the defined function.
 import os
 import datetime
 import math
+
 import FreeCAD as App
-from FreeCAD import Vector
 import Draft
+from FreeCAD import Vector
 from draftutils.messages import _msg, _wrn
-import draftobjects.arc_3points
 
 if App.GuiUp:
     import DraftFillet
@@ -172,9 +172,9 @@ def create_test_file(file_name="draft_test_objects",
 
     _msg(16 * "-")
     _msg("Circular arc 3 points")
-    draftobjects.arc_3points.make_arc_3points([Vector(4600, 0, 0),
-                                               Vector(4600, 800, 0),
-                                               Vector(4000, 1000, 0)])
+    Draft.make_arc_3points([Vector(4600, 0, 0),
+                            Vector(4600, 800, 0),
+                            Vector(4000, 1000, 0)])
     t_xpos += 600
     _t = Draft.makeText(["Circular arc 3 points"], Vector(t_xpos, t_ypos, 0))
     _set_text(_t)

src/Mod/Draft/drafttests/test_creation.py

@@ -133,8 +133,7 @@ class DraftCreation(unittest.TestCase):
         _msg("  a={0}, b={1}".format(a, b))
         _msg("  c={}".format(c))
 
-        import draftobjects.arc_3points as arc3
-        obj = arc3.make_arc_3points([a, b, c])
+        obj = Draft.make_arc_3points([a, b, c])
         self.assertTrue(obj, "'{}' failed".format(operation))
 
     def test_ellipse(self):