Add sparseCheckout symbol for Pipeline

[MarkEWaite]

Add sparseCheckout symbol for Pipeline

Add the sparseCheckout symbol for Pipeline so that users do not need to use the old $class syntax.

Includes a test that confirms the sparseCheckout syntax works as expected.

Testing done

Tested interactively to confirm that the new symbol behaves the same as the old syntax behaved. Does not include detailed functional testing that the sparseCheckout symbol works as expected, since there are already tests of sparse checkout in other tests.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue