[MSSQL][DB2] Add support for XML data type

[DavideD]

Based on the documentation, the xml data type is not supported in MSSQL. Example of column definition:

xmlColumn xml

It currently throws (during a select sql query):

Caused by: java.lang.UnsupportedOperationException: Unable to decode typeInfo for XML
	at io.vertx.mssqlclient.impl.codec.DataType.decodeTypeInfo(DataType.java:1065)
	at io.vertx.mssqlclient.impl.codec.MSSQLCommandCodec.handleColumnMetadata(MSSQLCommandCodec.java:120)
	at io.vertx.mssqlclient.impl.codec.MSSQLCommandCodec.decode(MSSQLCommandCodec.java:51)
	at io.vertx.mssqlclient.impl.codec.TdsMessageDecoder.decodeMessage(TdsMessageDecoder.java:75)
	at io.vertx.mssqlclient.impl.codec.TdsMessageDecoder.channelRead(TdsMessageDecoder.java:47)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
	... 20 more

I've created this issue for SqlServer but Db2 has the same problem.