Use a power-of-two value for Primary Grid Steps in the 3D editor

This matches the 2D editor default behavior.

Powers of two are usually better for grid divisions as they are often
used in level design.

(cherry picked from commit 31cf3e2572e7c6db9ac8a58d16e289be69967b7c)

editor/editor_settings.cpp

@@ -511,7 +511,8 @@ void EditorSettings::_load_defaults(Ref<ConfigFile> p_extra_config) {
 	_initial_set("editors/3d/secondary_grid_color", Color(0.38, 0.38, 0.38, 0.5));
 
 	// If a line is a multiple of this, it uses the primary grid color.
-	_initial_set("editors/3d/primary_grid_steps", 10);
+	// Use a power of 2 value by default as it's more common to use powers of 2 in level design.
+	_initial_set("editors/3d/primary_grid_steps", 8);
 	hints["editors/3d/primary_grid_steps"] = PropertyInfo(Variant::INT, "editors/3d/primary_grid_steps", PROPERTY_HINT_RANGE, "1,100,1", PROPERTY_USAGE_DEFAULT);
 
 	// At 1000, the grid mostly looks like it has no edge.