IReadOnlyList<T> for options list

I'd like to suggest list options support more than just `IEnumerable` properties. `IEnumerable` is not a great choice for list properties because it hides information about the underlying collection (order, count).

Adding support for `IReadOnlyList` would be very helpful because it is both ordered (supports an indexer), and has a count. Support for arrays, `ICollection`, `List`, `IList`, `IReadOnlyCollection` are also things that could be considered.

Start by locating the option-property handling for IEnumerable and trace how list values are parsed. Compare the requested IReadOnlyList behavior with arrays, ICollection, List, IList, and IReadOnlyCollection. The work is done when the supported collection types have defined, consistent option behavior and coverage for the requested cases.

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