Configure prettier to run on the whole repo

[justinhaaheim]

This PR configures prettier so it runs on all js/ts/json files, not just the ones in src/locales, to make the code more uniformly formatted.

To do that we move the prettier config to .prettierrc.js so that the prettier CLI, vscode and other editors can access it for things like formatOnSave. Previously running prettier --write . or prettier --check . from the command line would use the default prettier config, ignoring what was in .eslintrc.js.

It also adds a workspace vscode config that contains a launch script to debug the app, and, notably, a settings config that turns on formatOnSave by default. I submit that this is a preferable way to code, since it doesn't require the engineer to fix things manually or run a fix script to handle simple formatting.

If we're a thumbs up on this change I'll add a commit that runs prettier on the whole repo before merging to handle any existing formatting issues.

[jaraco]

This issue has affected me too when I was getting failing checks locally but not in CI.