Viewport: Add toggle for edit mode overlays fresnel

Adds a userpref toggle for the edit mode overlays fresnel.
The edit mode fresnel is only a bit useful in edge cases, like
very dense photogrametry, and the problem is that it causes
more eye strain when modeling for many hours. And it's
benefit on shape readability is small compared to it's negative
impact on selection visibility. It makes the selection color to a
darker less saturated color instead of the theme color, which
leads to worse contrast between the selection and the mesh
or with the background, and also makes the unselected (black)
brighter, also reducing contrast. So it's off by default.

This was split up from https://projects.blender.org/blender/blender/pulls/110097

Pull Request: https://projects.blender.org/blender/blender/pulls/111494

scripts/startup/bl_ui/space_userpref.py

@@ -741,6 +741,10 @@ class USERPREF_PT_viewport_display(ViewportPanel, CenterAlignMixIn, Panel):
         if view.mini_axis_type == 'GIZMO':
             col.prop(view, "gizmo_size_navigate_v3d", text="Size")
 
+        layout.separator()
+        col = layout.column(heading="Fresnel")
+        col.prop(view, "use_fresnel_edit")
+
 
 class USERPREF_PT_viewport_quality(ViewportPanel, CenterAlignMixIn, Panel):
     bl_label = "Quality"