Add support for many-to-many relations without navigation property

[momvart]

Sometimes, it happens that we are only interested in one side of a many-to-many relationship. So, there would be only one navigation property in one of the entries.

Example:

public class Widget 
{
    public int Id { get; set; }
    public string Name { get; set; }
}
public class User
{
    public int Id { get; set; }
    public string Username { get; set; }
    public ICollection<Widget> StarredWidgets { get; set; }
}

This is a question asked on stackoverflow and the accepted answer is this which uses an empty version of WithMany (Entity Framework):

modelBuilder.Entity<User>()
    .HasMany(u => u.StarredWidgets)
    .WithMany() // <- no parameter here because there is no navigation property
    .Map(m =>
    {
        m.MapLeftKey("UserId");
        m.MapRightKey("WidgetId");
        m.ToTable("UserWidgets");
    });

Is it possible to add support for defining this kind of relationship?

[ajcvickers]

Duplicate of #3864. Make sure to vote for that issue!