make units other than data work for axes labels and title (bug #35857) * graphics.in.h, graphics.cc (base_property::invalidate): New function. (axes::properties::set_defaults): If mode is not "reset", invalidate label and title handles before recreating them. Don't notify toolkit when recreating label and title handles. Update label and title positions after they are created. (convert_label_position): New static function. (axes::properties::update_xlabel_position, axes::properties::update_ylabel_position, axes::properties::update_zlabel_position, axes::properties::update_title_position): Return early if object is not valid. Call convert_label_position to handle units other than "data". (text::properties::update_units): Preserve "auto" positionmode. (gh_manager::do_make_graphics_handle): Call override_defaults here for newly created objects. If creating an axes object, also call override_defaults for the axes label and title objects. (graphics_object::override_defaults): New function. (figure::figure, axes::axes, line::line, text::text, image::image, patch::patch, surface::surface, hggroup::hggroup, uimenu::uimenu, uicontextmenu::uicontextmenu, uicontrol::uicontrol, uipanel::uipanel, uitoolbar::uitoolbar, uipushtool::uipushtool, uitoggletool::uitoggletool): Don't call override_defaults from constructor.