Improve list iteration

[tpluscode]

I was just handling an RDF List and I notice that it returns only an iterator of pointers. I would like to propose to extend it with additional getters which would likewise iterate terms and and values, similarly to how a pointer itself has the .terms and .values properties.

This will allow for simpler usage, like when doing spread and map. For example, trying to get all unique terms from a list

import TermSet from '@rdfjs/term-set'

let listPointer

-const set = new TermSet([...excludedPointer.list()].map(({ term }) => term))
+const set = new TermSet([...excludedPointer.list().terms])