Well, the idea of the menu system is to give plugins the ability to add their own actions to predefined menus (like the page tools). Adding buttons individually to the template defeats that purpose.
But of course it's still possible. You can simply instantiate the appropriate Item and use it's methods to output some default HTML or use it's properties to create your own HTML.
The equivalent of <?php tpl_button('edit')?>
would be echo (new dokuwiki\Menu\Item\Edit())->asHtmlButton();