Add support for testcase.attachments

[bryanbcook]

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

• [ ] Cucumber
• [x] JUnit
• [x] MSTest
• [x] 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:

• 49