refactor: formalize deep link opt in

[johallar]

Address #588 (comment) by formalizing how state gets added to the encoded deep linking state.

Idea:
add a function to encodeState, which will allow devs to add an atom, specify the property name in deep link state, and specify how the state should be added to the object

eg:

encodeState({
    prop: (deepLinkState) => return deepLinkState.dag.operatorNodeIds, // how to do this well w nested object
    get: () => [...store.get(selectedNodeIdsAtom)].sort(),
 })