I don't know why such an important feature is so hidden, but I can't find anything. The option on the right-click menu, as seen in this blog post, does not seem to exist anymore. The manual does not appear to contain a page about hierarchies. The properties panel of objects does not contain any options related to hierarchies.
How do you make a hierarchy? Is it only possible through runtime events now?
EDIT: It turns that apparently the only way to use hierarchies in the layout is to select multiple objects at once, then click on the object you want the parent to be. Only then will the hierarchies option appear in the right-click menu; I don't believe the blog post linked above made this very clear. Either way, here it is for anyone who needs it in the future.