CSHARP-5734: Update doc comments for IBsonIdProvider GetDocumentId method

Author: rstam

src/MongoDB.Bson/Serialization/IBsonIdProvider.cs

@@ -29,7 +29,7 @@ public interface IBsonIdProvider
         /// <param name="id">The Id.</param>
         /// <param name="idNominalType">The nominal type of the Id.</param>
         /// <param name="idGenerator">The IdGenerator for the Id type.</param>
-        /// <returns>True if the document has an Id.</returns>
+        /// <returns>True if the document has an Id field (regardless of the value).</returns>
         bool GetDocumentId(object document, out object id, out Type idNominalType, out IIdGenerator idGenerator);
 
         /// <summary>