Add NUnit Test handling for PSScriptAnalyzer results (#211)

This will now convert the output of `Invoke-ScriptAnalyzer` into an NUnitXml file that can then be published through the CI system so that we can fail on ScriptAnalyzer failures, as well as easily
see them in the test output.

Got the initial idea for this approach from @MathieuBuisson's [blog post](https://mathieubuisson.github.io/psscriptanalyzer-first-class-citizen/) (which directly converted the ScriptAnalyzer results into an NUnit XML file, but only had a single passing test for the success scenario).  I then combined that idea with one from a [Dr. Scripto post](https://devblogs.microsoft.com/scripting/psscriptanalyzer-deep-dive-part-3-of-4/) which used Pester to invoke PSScriptAnalyzer, ensuring that there was a test created for each possible Rule.  The problem with the Dr. Scripto approach was that multiple failures of the same rule still resulted in a single failure, and the test output lost the actual message from ScriptAnalyzer.

I ended up implementing this differently than Mathieu, directly working with the XML class to build up the XML document, but really appreciated the initial ideas that he had with this approach.

Sample build test result when there was a Script Analysis failure: https://dev.azure.com/ms/PowerShellForGitHub/_build/results?buildId=84441&view=ms.vss-test-web.build-test-results-tab

Author: HowardWolosky

build/pipelines/templates/run-staticAnalysis.yaml

@@ -11,4 +11,18 @@ steps:
   - powershell: |
        $results = Invoke-ScriptAnalyzer -Path ./ –Recurse
        $results | ForEach-Object { Write-Host "##vso[task.logissue type=$($_.Severity);sourcepath=$($_.ScriptPath);linenumber=$($_.Line);columnnumber=$($_.Column);]$($_.Message)" }
+
+       $null = New-Item -Path ..\ -Name ScriptAnalyzer -ItemType Directory -Force
+       ./build/scripts/ConvertTo-NUnitXml.ps1 -ScriptAnalyzerResult $results -Path ../ScriptAnalyzer/test-results.xml
+    workingDirectory: '$(System.DefaultWorkingDirectory)'
     displayName: 'Run Static Code Analysis (PSScriptAnalyzer)'
+
+  - task: PublishTestResults@2
+    displayName: 'Publish ScriptAnalyzer Test Results'
+    inputs:
+      testRunTitle: 'Windows Test Results for PSScriptAnalyzer'
+      buildPlatform: 'Windows'
+      testRunner: NUnit
+      testResultsFiles: '../ScriptAnalyzer/test-results.xml'
+      failTaskOnFailedTests: true # required to fail build when tests fail
+    condition: succeededOrFailed()