The script `./scripts/frontend/compile_css.mjs` compiles our SCSS style
code to CSS. It follows the same rules/settings that our sassc-rails gem
currently does (compiling the same files) while using dart sass and not
the deprecated C implementation.

Compiled CSS files will be placed in `app/assets/builds` where they can
be picked up by the `cssbundling` gem. The gem _needs_ runs the npm
script `build:css`.

We also mark `sass` as a production dependency so that our license
scanning picks up everything properly.

One more note, the current MR doesn't integrate with the Vite and
Webpack dev servers yet, this would be done in a second step.

For more context see the in-progess MR:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/140611



Co-Authored-By: Muhammed Ali <muhammed.ali@airtimerewards.com>