Fix "map" attribute when serializing template properties to XML

This commit adds missing map attribute to manifest XML serialization. For example:

<data name="PacketDirection" inType="win:UInt32" map="DirectionMap"/>

from Microsoft-Windows-WFP

The map attribute returned by Microsoft at least in:

using Microsoft.Diagnostics.Tracing.Parsers;
RegisteredTraceEventParser.GetManifestForRegisteredProvider("Microsoft-Windows-WFP");