CSHARP-5442: Atlas Search doesn't respect the correct serializer

src/MongoDB.Driver/FieldValueSerializerHelper.cs

@@ -141,18 +141,6 @@ public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSer
             return ConvertIfPossibleSerializer.Create(valueType, fieldType, fieldSerializer, serializerRegistry);
         }
 
-        public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSerializer, IBsonSerializerRegistry serializerRegistry, Type valueType, object value)
-        {
-            if (!valueType.GetTypeInfo().IsValueType && value == null)
-            {
-                return fieldSerializer;
-            }
-            else
-            {
-                return GetSerializerForValueType(fieldSerializer, serializerRegistry, valueType, allowScalarValueForArrayField: false);
-            }
-        }
-
         // private static methods
         private static bool HasStringRepresentation(IBsonSerializer serializer)
         {
@@ -313,7 +301,7 @@ public override void Serialize(BsonSerializationContext context, BsonSerializati
             }
         }
 
-        internal class IEnumerableSerializer<TItem> : SerializerBase<IEnumerable<TItem>>
+        internal class IEnumerableSerializer<TItem> : SerializerBase<IEnumerable<TItem>>, IBsonArraySerializer
         {
             private readonly IBsonSerializer<TItem> _itemSerializer;
 
@@ -351,6 +339,12 @@ public override void Serialize(BsonSerializationContext context, BsonSerializati
                     bsonWriter.WriteEndArray();
                 }
             }
+
+            public bool TryGetItemSerializationInfo(out BsonSerializationInfo serializationInfo)
+            {
+                serializationInfo = new BsonSerializationInfo(null, _itemSerializer, typeof(TItem));
+                return true;
+            }
         }
 
         internal class NullableEnumConvertingSerializer<TFrom, TTo> : SerializerBase<Nullable<TFrom>> where TFrom : struct where TTo : struct

src/MongoDB.Driver/IAggregateFluent.cs

@@ -404,7 +404,6 @@ IAggregateFluent<TNewResult> Lookup<TForeignDocument, TAsElement, TAs, TNewResul
         IAggregateFluent<BsonDocument> SetWindowFields<TWindowFields>(
             AggregateExpressionDefinition<ISetWindowFieldsPartition<TResult>, TWindowFields> output);
 
-        //TODO If I add a parameter here, then this would be a binary breaking change
         /// <summary>
         /// Appends a $search stage to the pipeline.
         /// </summary>