Add support for testcase.attachments

[bryanbcook]

This PR introduces extends testcase with an attachments array. Currently supported for the following implementations:

• Cucumber
• JUnit
• MSTest
• NUnit
• XUnit (not supported)

A few implementation notes:

• JUnit:

  Based on the Jenkins Plugin Attachment plugin which inspects the <system.out> property in the XML for the following syntax: [[ATTACHMENT|/absolute/path/tofile.png]]

  I have confirmed that the azure-devops build-agent test publisher uses this convention as well. The path can be an absolute path or relative to the location of the test results xml.

  

• MSTest:

  Attachments appear in the xml under the test result for a given execution:

  <TestRun name="username_machinename 2024-02-28 17:25:00">
    <Results>
      <UnitTestResult executionId="xxxx" testId="yyyy">
        <ResultFiles>
          <ResultFile path="machinename/file.txt" />
        </ResultFiles>
       </UnitTestResult>
    </Results>
    <TestDefinitions>
      <UnitTest id="yyyy">
      </UnitTest>
    </TestDefinitions>
  </TestRun>

  Calls to TestContext.AddResultFile(filename) copies the file into a special folder per test, which is a combination of TestRun name + Test Execution id + Machine Name, relative to the location of the test results xml file.

  testResults.trx
  \<username>_<machinename>_<timestamp>
    \In
      \<testexecutionid>
        \<machinename>
          file.txt
  

  The test-parser mstest implementation expands out the relative path from the XML into a value that can be resolved at runtime relative to the test results xml file.

• NUnit:

  Very straight-forward as NUnit only accepts absolute paths.

Addresses:

• Proposal: Add support for attachments #49