pdf: migrate to flat config

Using npx @eslint/migrate-config .eslintrc.json
Then add the additional packages needed
(@eslint/compat, globals, @eslint/eslintrc, @eslint/js)
Add paths from the .gitignore file to the ignored patterns.
Remove the options from the call to eslint which are not
supported anymore in the package.json.
Also run mjs files through the prettier.

Issue: ecamp#5282