feat(SidebarToggleButton): allow setting custom icons

        let icon = if collapsed {
            if self.side.is_left() {
                IconName::PanelLeftOpen
            } else {
                IconName::PanelRightOpen
            }
        } else {
            if self.side.is_left() {
                IconName::PanelLeftClose
            } else {
                IconName::PanelRightClose
            }
        };