UI: Use the 3D cursor icon for the RNA struct

Since there is a specific icon to represent the 3D cursor it makes sense
to add it to the RNA struct. This struct's icon is only displayed in the
Data API section of the outliner.

source/blender/makesrna/intern/rna_scene.c

@@ -2821,6 +2821,7 @@ static void rna_def_view3d_cursor(BlenderRNA *brna)
   RNA_def_struct_sdna(srna, "View3DCursor");
   RNA_def_struct_path_func(srna, "rna_View3DCursor_path");
   RNA_def_struct_ui_text(srna, "3D Cursor", "");
+  RNA_def_struct_ui_icon(srna, ICON_CURSOR);
 
   prop = RNA_def_property(srna, "location", PROP_FLOAT, PROP_XYZ_LENGTH);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);