Unreported fix: vertex colors overlay not set for new 3d views.

Found during researching {T86956}.

source/blender/makesdna/DNA_view3d_defaults.h

@@ -70,6 +70,7 @@
  \
     .gpencil_paper_opacity = 0.5f, \
     .gpencil_grid_opacity = 0.9f, \
+    .gpencil_vertex_paint_opacity = 1.0f, \
   }
 
 #define _DNA_DEFAULT_View3DCursor \

source/blender/makesrna/intern/rna_space.c

@@ -4492,7 +4492,6 @@ static void rna_def_space_view3d_overlay(BlenderRNA *brna)
   prop = RNA_def_property(srna, "gpencil_vertex_paint_opacity", PROP_FLOAT, PROP_FACTOR);
   RNA_def_property_float_sdna(prop, NULL, "overlay.gpencil_vertex_paint_opacity");
   RNA_def_property_range(prop, 0.0f, 1.0f);
-  RNA_def_property_float_default(prop, 1.0f);
   RNA_def_property_ui_text(prop, "Opacity", "Vertex Paint mix factor");
   RNA_def_property_update(prop, NC_SPACE | ND_SPACE_VIEW3D, "rna_GPencil_update");
 }