Feat: Treeview link/toggle split

[NickDJM]

Summary

In the APG, you can click the link of a treeview and it take you to a page and then click the dropdown arrow specifically to activate the submenu.

This isn't actually in the interaction guidelines as far as I can tell, but it is mentioned in the body text. I'd like to implement this asap since a client needs it.

Solution

Add an option to split treeviews (or just make treeviews do this by default).

It's possible this might be a breaking change, so 5.x might come sooner than anticipated.

Additional context

https://www.w3.org/WAI/ARIA/apg/patterns/treeview/examples/treeview-navigation/