Set() should throw for owned types

[AndriySvyryd]

From dotnet/EntityFramework.Docs#1168 by @voroninp

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;

namespace EfCore22.OwnedTypes
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var ctx = new TestContext())
            {
                ctx.Database.EnsureCreated();
                ctx.Add(new Order { Items = { new OrderItem { Name = "Just an item." } } });
                ctx.SaveChanges();
            }

            using (var ctx = new TestContext())
            {
                var items = ctx.Set<OrderItem>().ToList();
                Console.WriteLine($"I managed to successfully get '{items.Count}' order items.");
            }

            Console.ReadKey();
        }
    }

    public class Order
    {
        public int Id { get; set; }
        public List<OrderItem> Items { get; } = new List<OrderItem>();
    }

    public class OrderItem
    {
        public string Name { get; set; }
    }

    public class TestContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer("Server=(localdb)\\MSSQLLocalDB;Database=OwnedTypes");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Order>(b =>
            {
                b.OwnsMany(m => m.Items, ob =>
                {
                    ob.Property<int>("Id")
                        .IsRequired()
                        .ValueGeneratedOnAdd();

                    ob.HasForeignKey("OrderId");

                    ob.HasKey("Id", "OrderId");
                    ob.ToTable("OrderItems");

                });
            });
        }
    }
}