Migration Snapshot enum/valueconverter issue

Describe what is not working as expected.

If you have a nullable enum property that also uses a value converter, the snapshot code generates invalid calls.

    public enum RoadwaySides
    {
        Left = -1,
        Center,
        Right
    }

    public class ProjectDetail
    {
        public RoadwaySides? RoadwaySide { get; set; }
    }

... in model builder

            builder.Property(pd => pd.RoadwaySide).HasConversion(v => v == RoadwaySides.Left ? "L" : v == RoadwaySides.Center ? "C" : v == RoadwaySides.Right ? "R" : null, v => v == "L" ? RoadwaySides.Left : v == "C" ? RoadwaySides.Center : v == "R" ? RoadwaySides.Right : (RoadwaySides?)null).HasColumnName("RDWYSIDE").HasColumnType("char(1)").HasMaxLength(1);

... in generated snapshot

                    b.Property<int?>("RoadwaySide")
                        .HasConversion(new ValueConverter<RoadwaySides?, string>(v => default(string), v => default(RoadwaySides?)))
                        .HasColumnName("RDWYSIDE")
                        .HasColumnType("char(1)")
                        .HasMaxLength(1)
                        .IsUnicode(false);

The snapshot generator unwraps the enum for the property call but does not unwrap the enum for the HasConversion call.

I think this line:
https://github.com/aspnet/EntityFrameworkCore/blob/dev/src/EFCore.Design/Migrations/Design/CSharpSnapshotGenerator.cs#L433

needs a .UnwrapEnumType() call in it to fix the problem.

Further technical details

EF Core version: 2.1.0 - 28148
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Win10 Ent
IDE: Visual Studio comm 2017 15.4