Cosmos: ReadItem should be used for Reload

[ajcvickers]

Same repro code as for #33881. Do:

await context.Entry(x).ReloadAsync();

This could be a ReadItem, but is actually:

      SELECT VALUE {"Id" : c["Id"], "Discriminator" : c["Discriminator"], "Title" : c["Title"], "id0" : c["id"], "" : c}
      FROM root c
      WHERE ((c["Discriminator"] = "Post") AND (c["Id"] = @__p_0))
      OFFSET 0 LIMIT 1

[roji]

This is effectively a special case of #34163, which is about using ReadItem when a projection is present, i.e. the whole entity isn't getting projected out (will keep this open to track as a separate user-facing scenario).

The incoming query generated by Reload:

DbSet<Item>()
    .AsNoTracking()
    .IgnoreQueryFilters()
    .Where(e => EF.Property<int>(e, "Id") == __p_0 && EF.Property<string>(e, "PartitionKey") == __p_1)
    .Select(e => new object[]
    { 
        (object)(int)EF.Property<int>(e, "Id"), 
        (object)(string)EF.Property<string>(e, "PartitionKey"), 
        (object)(string)EF.Property<string>(e, "Discriminator"), 
        (object)(string)EF.Property<string>(e, "__id"), 
        (object)(JObject)EF.Property<JObject>(e, "__jObject") 
    })
    .FirstOrDefault()