Fix content_scripts not working in production

[cezaraugusto]

Fix #166

This bug often pops up but hopefully this is a permanent fix. In webpack we use style-loader for dev and mini-css-extract-plugin for prod. In prod the content_script styles are emitted but we never reference them in the manifest. This PR fixes it.

Test plan is mostly running "build" in your favorite content_* and new_* templates and assert CSS works both in dev and prod.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

see 5 files with indirect coverage changes

[pkg-pr-new]

Open in Stackblitz

pnpm add https://pkg.pr.new/extension-js/extension.js/extension@172

pnpm add https://pkg.pr.new/extension-js/extension.js/extension-create@172

pnpm add https://pkg.pr.new/extension-js/extension.js/extension-develop@172

commit: 68e3189

[cezaraugusto]

@OSpoon I'm going to merge this one for the next hotfix release but please report if I'm wrong