Add support for filtering by enum property types

[kzu]

Given the following entity:

public enum BookFormat { Paperback, Hardback }

public record Book(string ISBN, string Title, string Author, BookFormat Format);

The following query should Just Work™:

await foreach (var info in from book in repo.CreateQuery()
                            where book.Format == BookFormat.Hardback
                            select new { book.ISBN, book.Title })
{
}

Note that this does not work in the built-in TableQuery<T> in CosmosDB :).