Lint static files and dependencies with eslint + knip

[KevinMind]

Fixes: mozilla/addons#15482

Description

add eslint + knip + styleline to handle code style and formatting

Context

Ensure our static files are high quality with stricter linting rules. All of the changes in the ./static directory are a result of automated formatting or light manual changes when automatic formatting didn't work.

This PR will be too big to review, but you can scan the commits to see how each tool is introduced in a pattern:

• add the tool, silencing any rules that cause errors
• apply each rule one at a time fixing the errors

Javascript

We already used prettier for formatting, but eslint includes a more robust set of checks and extendable rules. Additionally prettier can be run via eslint, so there's still just one tool to call. Finally, knip is useful for identifying "dead code" that is not imported or used anywhere.. as you can see we had a fair bit of that.

Re-writing the config files in .ts just makes them a lot easier to validate while editing them as vscode will give you the type errors. Again, as you can see, there were invalid properties there that were previously missed.

Finally, zod gives syntax and runtime validation of our environment variables. Ensures you cannot run the build without valid parameters defined in the environment.

LESS/CSS

Using styleline I used the same approach as for JS, applied each rule one at a time to make it clear exactly what is changing why.

Testing

Test that addons-server can run addons-linter by verifying file upload works with validation as expected.

You can test the linting by:

• breaking some css or js using invalid syntax like referencing an undefined variable in a file
• add an npm dependency that is not used npm i react -S
• add a js/css file that is not imported anywhere in ./static/js|css directories.

Run make lint and expect knip to show errors in each case.

Finally, you can test that knip will fix it's mistakes. After adding the additional dead code/deps run make format and knip should remove the files and dependency from package.json. The undefined variable may or may not be fixed automatically but if you "unformat" some code it should be reformatted.

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[KevinMind]

Rebased after merging the vite cleanup

[diox]

@KevinMind wrong issue linked ?

[KevinMind]

Rebased version #23230

[KevinMind]

Closed in favor of #23229