Bottleneck reading XML element value

Up to 40-50% of the time can be spent in this method
https://github.com/carlossanlop/DocsPortingTool/blob/main/Libraries/XmlHelper.cs#L134-L143

It is simply reading the value of an element, but it needs to do it literally, ie., any CDATA wrapping it, etc, so it can't just get Value. This forces creating an Xml text writer, etc - it's very slow.

I added in a comment there an alternative way of doing this based on the stackoverflow post below

https://stackoverflow.com/questions/3793/best-way-to-get-innerxml-of-an-xelement

I didn't try every scenario but it seems to produce the same result albeit with sometimes different line wraps (possibly an improvement). It's about twice as fast so if it's good enough it could be swapped for what is there now.