triangulate modifier: beauty option

It works fine in my tests here.
There is a chance I need to tag inside BM_mesh_beauty_fill because the new edges that may not carry the old edge flag.

It would be something like (under an 'if use_tag' perhaps)

```diff
+++ b/source/blender/bmesh/tools/bmesh_beautify.c
@@ -421,6 +421,11 @@ void BM_mesh_beautify_fill(BMesh *bm, BMEdge **edge_array, const int edge_array_
                                BMO_elem_flag_enable(bm, e->l->f, FACE_MARK | ELE_NEW);
                                BMO_elem_flag_enable(bm, e->l->radial_next->f, FACE_MARK | ELE_NEW);
                        }
+                       else {
+                               BM_elem_flag_enable(e, BM_ELEM_TAG);
+                               BM_elem_flag_enable(e->l->f, BM_ELEM_TAG);
+                               BM_elem_flag_enable(e->l->radial_next->f, BM_ELEM_TAG);
+                       }
                }
        }
```