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Purpose

REVIT-141868
DynamoRevit 2.x Categories Dropdown Produces Inconsistent Results Between Revit versions.
Also fixes DynamoDS/DynamoRevit#2281

I believe this is a more complete version of what you're trying to achieve. @ZiyunShang Let me know how you want to cooperate this task

TODOs:

• Add Json Unit tests
• Add XML Unit tests
• Testing undo redo

"Nodes": [
    {
      "ConcreteType": "DSRevitNodesUI.Categories, DSRevitNodesUI",
      "SelectedIndex": 6,
      "SelectedString": "OST_DuctTerminal",
      "NodeType": "ExtensionNode",
      "Id": "e16b9ac4ad604e7eb4d29a7975335d7c",
      "Inputs": [],
      "Outputs": [
        {
          "Id": "ac2e1b04ef994a4fb5dbe4b2855d1097",
          "Name": "Category",
          "Description": "The selected Category.",
          "UsingDefaultValue": false,
          "Level": 2,
          "UseLevels": false,
          "KeepListStructure": false
        }
      ],
      "Replication": "Disabled",
      "Description": "All built-in categories."
    }
  ]

I have did my manual testing in three basic cases:

• Using master build, place a categories node into canvas and save
• Using master build, opening a DYN saved in Dynamo 2.1.0 w/ R2020 worked
• Using master build, opening a DYN saved in Dynamo 1.3.3 w/ R2019 worked
  

Declarations

Check these if you believe they are true

• The code base is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning, and are documented in the API Changes document.

Reviewers

@mjkkirschner @ZiyunShang

FYIs