ESLint changes preparing for Prettier

[shadowspawn]

Pull Request

Problem

ESLint have deprecating the formatting rules, and suggest using a separate formatter.

Using StandardJS and TypeScript equivalent has been painful to maintain. (To be fair, partly because of how we ended up using it.)

See: #2104

Solution

Use ESLint for linting. Start with ESLint recommended rules.

Use Prettier for formatting. In a way this is quite like using Standard, opinionated so less setup and debate over settings! Installed and configured in this PR, but not used to format files yet to keep the PR focused on the setup changes.

I did a rework of the naming of the npm scripts so now check lint/format/type, and fix lint/format.

Note: I saw there was a new flat config for ESLint and liked the look of it. Flat config is going to be default in ESLint 9. I used the new config file name eslint.config.js so detected as flat from command-line with ESLint 8.

Note: eslint-plugin-jsdoc installed but not activated yet, as will complain about multiple issues. Have also installed prettier-plugin-jsdoc which will hopefully fix some of the lint issues! Will evaluate those in separate PR.

For interest, I found a good blog after doing most of the work: https://www.joshuakgoldberg.com/blog/configuring-eslint-prettier-and-typescript-together/

ChangeLog

[shadowspawn]

The Jest plugin has been updated with flat config support, so all the pieces are in place.

I could make a separate branch for the format/lint related PRs to land on so we run Prettier etc before affecting develop?

[shadowspawn]

The VSCode ESLint extension has flat config support by default available as a prerelease (can just switch to/from prerelease in extensions UX): microsoft/vscode-eslint#1644 (comment)

[abetomo]

Awesome!