[Tree] Finish up loose ends

[jpzwarte]

Provide a general summary of the issue here

• - Write more unit tests
• - Add ability to sort tree
• - Either get fix(lit-virtual): create Virtualizer instance before hostConnected TanStack/virtual#1061 merged, or create our own reactive controller
• - Update documentation

👤 Your name

Jeroen

🧢 Your Product/Team

SLDS