Add .vscodeignore

[AndreasArvidsson]

We get this warning from ci. Might be a good suggestion.

Run HaaLeo/publish-vscode-extension@v1
Specifically, running GitHub Action HaaLeo/[email protected].
Package the Extension
  Start packaging the extension.
  Warning: Neither a .vscodeignore file nor a "files" property in package.json was found. To ensure only necessary files are included in your extension, add a .vscodeignore file or specify the "files" property in package.json. More info: https://aka.ms/vscode-vscodeignore