Overlay: Add Wireframe overlay.

This overlay is showing mesh topology. It is usable with transparency
even if the mesh order can mess up with the expected result (some object
more prominent than others).

Edge thickness and alpha values are hardcoded for now but can easily be
added to theme or object settings.

release/scripts/startup/bl_ui/space_view3d.py

@@ -3593,6 +3593,7 @@ class VIEW3D_PT_overlay(Panel):
         col.prop(overlay, "show_all_objects_origin")
         col.prop(overlay, "show_relationship_lines")
         col.prop(overlay, "show_face_orientation")
+        col.prop(overlay, "show_wireframes")
         col.prop(overlay, "show_backface_culling")
 
         col = layout.column()