Overlay: Reduce retopology overlay default distance

Changes the default distance to something suitable for working on human
sized objects. The previous default required the object to be quite
massive in scale to look correct.

This not only improves the display but also makes accidental back facing
selection significantly less likely. There will be more cases where the
source object clips through the retopology, but this can also be helpful
as it shows where there are significant differences is the silhouette.
0.01 was chosen in Blender Chat as a nice round number that works for a
variety of objects.

See PR for comparison images.

Pull Request: https://projects.blender.org/blender/blender/pulls/137978

source/blender/blenloader/intern/versioning_defaults.cc

@@ -197,6 +197,8 @@ static void blo_update_defaults_screen(bScreen *screen,
       v3d->overlay.texture_paint_mode_opacity = 1.0f;
       v3d->overlay.weight_paint_mode_opacity = 1.0f;
       v3d->overlay.vertex_paint_mode_opacity = 1.0f;
+      /* Update default Z bias for retopology overlay. */
+      v3d->overlay.retopology_offset = 0.01f;
       /* Clear this deprecated bit for later reuse. */
       v3d->overlay.edit_flag &= ~V3D_OVERLAY_EDIT_EDGES_DEPRECATED;
       /* grease pencil settings */

source/blender/makesdna/DNA_view3d_defaults.h

@@ -41,7 +41,7 @@
     .flag = V3D_OVERLAY_VIEWER_ATTRIBUTE | V3D_OVERLAY_SCULPT_SHOW_MASK | V3D_OVERLAY_SCULPT_SHOW_FACE_SETS, \
     .wireframe_threshold = 1.0f, \
     .wireframe_opacity = 1.0f, \
-    .retopology_offset = 0.2f, \
+    .retopology_offset = 0.01f, \
     .viewer_attribute_opacity = 1.0f, \
     .xray_alpha_bone = 0.5f, \
     .bone_wire_alpha = 1.0f, \