Test API'ish way to change configuration settings

[jrieken]

Test for #1396

• any os - @Tyriar

Complexity 3

We added new API for writing configuration settings. Test the following

• update global and workspace configuration
• update config values that live in launch.json and/or task.json
• try to delete a value
• test the corner cases and make sure that you receive good error messages
  • try to update an in-existent value
  • try to update something with isn't a property but a property group (editor vs editor.tabSize)
  • try to update with invalid values, editor.tabSize = true

[jrieken]

FYI - to test against the latest API do the following:

• open your extensions package.json file
• change the engine.vscode property to *
• run npm run postinstall (assuming you have the vscode module as dev-dependency)
• undo the engine-version change from step 2