Cosmos: ReadItem should be used for Reload

Same repro code as for #33881. Do:

```C#
await context.Entry(x).ReloadAsync();
```
This could be a ReadItem, but is actually:

```sql
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
```