Union/Concat query with anonymous type and navigation property cannot be translated

Start with the LINQ repro in the issue and trace EF Core's query translation for Concat, anonymous projections, navigation-property access, and OrderBy. Done means the shown query translates and executes without the reported InvalidOperationException, with the behavior covered by a regression test if the relevant test location can be identified.

This query cannot be translated:

_ =
    ctx.TestChildren.Where(c => c.Name == "Child 1").Select(c => new { c })
        .Concat(ctx.TestChildren.Where(c => c.Name == "Child 2").Select(c => new { c }))
        .Select(x => new { x.c, x.c.TestParent }) //Use c.TestParent
        .OrderBy(x => x.TestParent.Name) //Avoid client evaluation
        .ToList();
        
//

public partial class TestChild
{
    public int ID { get; set; }
    public int? TestParentID { get; set; }
    public string Name { get; set; }

    public virtual TestParent TestParent { get; set; }
}

public partial class TestParent
{
    public TestParent()
    {
        TestChildren = new HashSet<TestChild>();
    }

    public int ID { get; set; }
    public string Name { get; set; }

    public virtual ICollection<TestChild> TestChildren { get; set; }
}

System.InvalidOperationException: 'The LINQ expression 'DbSet<TestChild>()
    .Where(t => t.Name == "Child 1")
    .Select(t => new { c = t })
    .Concat(DbSet<TestChild>()
        .Where(t0 => t0.Name == "Child 2")
        .Select(t0 => new { c = t0 }))
    .OrderBy(e => e.c.TestParent.Name)' could not be translated. Additional information: Translation of member 'TestParent' on entity type 'TestChild' failed. Possibly the specified member is not mapped.
Translation of member 'TestParent' on entity type 'TestChild' failed. Possibly the specified member is not mapped. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.'

The repro depends on multiple properties of the query:

1. Concat must be used.
2. The sources for the concat must be wrapped in an anonymous type.
3. The c.TestParent member must be accessed.
4. I added an OrderBy to avoid client evaluation. If this is not done then c.TestParent is simply evaluated on the client in the final Select.

So the following does not throw:

_ =
    ctx.TestChildren.Where(c => c.Name == "Child 1")
        .Concat(ctx.TestChildren.Where(c => c.Name == "Child 2")) //Concat source not wrapped
        .Select(x => new { x, x.TestParent })
        .OrderBy(x => x.TestParent.Name) //Avoid client evaluation
        .ToList();

Tested in EF 5.0 preview 6.