Verify correct VS Code setup

[karlhorky]

A common problem that happens to students is that they have not set up VS Code correctly, which leads to problems with Prettier not formatting code files.

Let's add some automated checks to make sure that students get it set up properly

Some ideas for setting this up:

• Add System Setup instructions for validating the JSON from the settings (or check in Preflight / ESLint setup?)
• Add prettier.config.json file with same defaults we use to ESLint, add to install script
• Create test project for VS Code settings and extensions
• Create screenshot in system setup guide showing correct setup with test project, with arrows pointing to Prettier, ESLint, and showing proper formatting on save
• Add step to System Setup guide for creating "projects" directory and cloning test project, with screenshot of how the editor should look