Feature/xpath transformer

[kashifsoofi]

Fixes #397 Added feature to select values from xml using XPath.
Implemented following as suggested

• XPath.SelectSingleNode
• XPath.SelectNodes
  Also implemented
• XPath.Evaluate

Reason for using OuterXml in HandleBarsXPath.cs is as follows but happy to change :
Testing

<todo-list>
  <todo-item id='a1'>abc</todo-item>
  <todo-item id='a2'>def</todo-item>
  <todo-item id='a3'>xyz</todo-item>
</todo-list>

with /todo-list/todo-item[1] results in <todo-item id="a1">abc</todo-item>
using https://www.freeformatter.com/xpath-tester.html. I think it is the correct behaviour as to select text I would provide /todo-list/todo-item[1]/text(). However same experssion return only the text using XPath2SelectSingleNode.

[codecov]

Codecov Report

Merging #398 into master will increase coverage by 0.27%.
The diff coverage is 98.63%.

@@            Coverage Diff             @@
##           master     #398      +/-   ##
==========================================
+ Coverage   79.91%   80.19%   +0.27%     
==========================================
  Files         122      123       +1     
  Lines        4809     4882      +73     
==========================================
+ Hits         3843     3915      +72     
- Misses        966      967       +1

Impacted Files	Coverage Δ
src/WireMock.Net/Transformers/HandleBarsHelpers.cs	100% <100%> (ø)	⬆️
src/WireMock.Net/Transformers/HandleBarsXPath.cs	98.61% <98.61%> (ø)

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[StefH]

Looks good.

Did you also test this new code in a real application/integration test ?

[kashifsoofi]

Looks good.

Did you also test this new code in a real application/integration test ?

Not yet.

[kashifsoofi]

Looks good.
Did you also test this new code in a real application/integration test ?

Not yet.

Tested and its working as expected.