feat: use tree enumerators

[bashbunni]

• feat: add Root option for lists
• refactor: use tree enumerators

When a list is used as the root of a list, it merges the items and inherits the name of the root list. Otherwise it looks like the sub-list belongs to the last element in the root list.

e.g.

This but imagine the "More Documents", etc are indented

Instead it looks like

Where the root tree's items are appended to the end of the list

[bashbunni]

Builds off of the other PR that adds the Title func to set a name for the list

[meowgorithm]

Looking good. Want to merge this with #338 so we can treat this as a general pass over tree/list? I think it'll be easier to reason about that way.

[bashbunni]

I think we should have the Indenter default to TreeIndenter when we set the Enumerator to list.Tree or list.RoundedTree. It feels weird having to specify that every time

[maaslalani]

Agreed!

[bashbunni]

🌴

[bashbunni]

Closing in favour of bringing trees out of internal #342