Add type-erased trait and support for shared AnyNodeRef across nodes (#14)

* feat(any-node-ref): type-erased node references with unified element support

* revert(docs): remove "the" article

* Cleanup

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Co-authored-by: geoffreygarrett <geoffrey@apollo.xyz>
Co-authored-by: Daniëlle Huisman <danielle@huisman.me>

Author: 3 people