Update to use new VSCode extension format

[kagof]

VSCode no longer should use the vscode module. This plugin needs to be updated to use the new module. It also greatly needs updates to resolve dependency security issues. I made a little bit of effort on this, but it seems not entirely trivial, and as far as I can tell VS Code hasn't published a very useful migration guide. The closest I can find is this: https://code.visualstudio.com/api/working-with-extensions/testing-extension#migrating-from-vscode