Rerun relationship discovery if target entity type has been readded

[AndriySvyryd]

modelBuilder
    .Entity<A>();

modelBuilder
    .Ignore<B>();

modelBuilder
    .Entity<B>();

Should find the relationship in:

public class A
{
    public int Id { get; set; }
    public B B { get; set; }
}

public class B
{
    public int Id { get; set; }
}

[AndriySvyryd]

Related to #18388