Refactor logic to construct the work item properties from the GitHub issue and associated projects (#447)

* First checkpoint: Initial refactoring

This commit makes some initial changes in the API, but no functional changes.

It helped crystallize the design to begin creating some tests.

* Checkpoint. Unit tests are all in place.

* Parent node calculations are correct

* Refactoring, part 1.

* Rework the extended properties.

Put all the computations for the work item properties in the constructor for the new type. Don't store user defined types, but the actual values used in the REST calls to Azure DevOps.

* Final bits of simplification

* Final refactoring

Make the constructor logic simpler

* Rename new class

Author: BillWagner

actions/sequester/ImportIssues/Program.cs

@@ -117,7 +117,6 @@ private static async Task<QuestGitHubService> CreateService(ImportOptions option
                 options.AzureDevOps.AreaPath,
                 options.ImportTriggerLabel,
                 options.ImportedLabel,
-                options.DefaultParentNode,
                 options.ParentNodes,
                 options.WorkItemTags);
     }