Recommend the CodeQL for VSCode extension

[dbartol]

I've added a .vscode/extensions.json file that will automatically recommend the CodeQL for Visual Studio Code extension to anyone who opens the repo in VS Code (without the extension already installed).

[jcreedcmu]

Assuming you've tested that it's acceptable to put json-with-javascript-esque comments here, this lgtm, but I'd feel a little safer with actual valid json, and documentation about what it's for being put in the commit message, which someone could still find in git history.

[dbartol]

Those comments are what VS Code itself generates when you run the Configure Recommended Extensions command, and it puts similar comments in settings.json, launch.json, etc. I've just added a .gitattributes in that directory to tell GitHub to allow the comments. Note that I've only added the .gitattributes for the .vscode directory, so it won't affect JSON used in, say, the javascript tests.

[dbartol]

(We already do the same thing at the root of vscode-codeql repo, because Rush likes to go overboard commenting its JSON configuration as well).

[jcreedcmu]

Yeah, that's convincing. I've generally noticed vscode to be pretty tolerant of comments in json, I just wanted to be adequately paranoid.