How to programatically create stuff?
Creating a plugin is a large task. I linked you to the top level so you could do your own research as you hadn't given much detail as to what tool you're working with or what you're trying to achieve.
By 'Visual Studio web tests' do you mean the Load/Performance tests that were recently deprecated in Visual Studio? i.e. this? https://docs.microsoft.com/en-us/visualstudio/test/quickstart-create-a-load-test-project?view=vs-2019
You can take a look at the Postman Importer source code as a starting point but yours may look very different.
I don't work for SmartBear so I can only speculate that importing competitors projects are not as sought by their customers as say supporting the latest and greatest technology. That being said you could make a feature requrest to SmartBear. They may be interested to implement this if there was enough people interested in making the switch.
