olevba, oleid: add detection for CustomXML parts

[decalage2]

See https://inquest.net/blog/2022/10/03/hiding-xml for an example of VBA macro using CustomXML to store a payload.

Also a new keyword ActiveDocument.CustomXMLParts to be added: https://learn.microsoft.com/en-us/office/vba/api/Office.CustomXMLParts

[mgeeky]

Another sample & vba snippet worth taking a look ¯_(ツ)_/¯

https://github.com/mgeeky/CustomXMLPart