Extract formatting / lint changes from the Error Recovery PR, and add prettier to ci / local tooling

[NullVoxPopuli]

Instead of: #1499

I figured it'd be better to extract the formatting changes from #1462

tl;dr:

• setup/update eslint / prettier on master
• squash feature/handle-error to single commit without merge
• cherry-pick lint/formatting files to feature/handle-error
• format / fix
• git rebase origin/master

The way this'll work is we have a one time cost of "run prettier / eslint --fix once" on master, and get things in a predictable spot -- then on the error-recovery branch, we'll rebase / squash down to one commit, copy the lint configs from this branch (as the error recovery branch doesn't have passing lints atm, and some stuff is TODO'd / disabled), then we can run lint:fix over there -- then finally rebase on top of master -- the goal is to reduce the diff from both branches by getting everything formatting / linting the same.

[NullVoxPopuli]

this file was invalid, it's been fixed (had duplicate keys)

[NullVoxPopuli]

formatting wasn't being checked on C.I.... 🙃

[chancancode]

👍 on doing this separately in a single pass, obviously I can’t/didn’t review every file, but as long as this is all automated and without code changes then let’s do it!

[wycats]

This is awesome! Thanks so much @NullVoxPopuli.

For future reference, the current formatting rules assume that you're running the equivalent of eslint --fix and then prettier -w to get the right formatting.

The eslint part does a lot of heavy lifting around imports and exports. Some of that heavy lifting is pure formatting (sorting, grouping, etc.) but eslint also enforces rules that mandate the use of import type when the import itself is unused as a value. This is essential to ensure that the code actually runs as intended at runtime and is also enforced (without fix support) via the verbatimModuleSyntax tsconfig setting.

In vscode, the expectation is that saving a file will automatically run both eslint fixes and prettier. The settings checked in to .vscode/settings.json, assuming the relevant extensions are installed, should make this happen automatically.