[ReflectionBasedXmlSerializer] To Support Types with IsSequence == true

[shmao]

Currently the reflection based method treat this kind of type as normal types. But potentially we can do some optimization for types that have ordered properties.

Searching #10586 in https://github.com/dotnet/corefx/blob/master/src/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs#L1181 would show the places to be fixed.