Convert list components to composites

[dqnykamp]

This PR refactors mathList, numberList, textList, and booleanList as composite components.

This change allows the list components to be used anywhere the singleton components are allowed, as they become a series of the singleton components. Components no longer have to treat the list components as a special case.

The PR introduces some backward-incompatible changes.

1. Individual components are no longer available from the .math, .number, etc., props. Instead, they are accessed directly using array notation off a reference to the component.
2. One can no longer construct a list where one entry depends directly on another entry.
3. It is no longer possible to distinguish between a list of one element and a singleton element, as the list of one element is turned into a single element.
4. It is no longer possible to represent an empty list, as an empty list just becomes nothing.

Resolves Doenet/DoenetTools#2265, resolves Doenet/DoenetTools#2215