Make SASS and rouge optional dependencies

I just started using Jekyll lately and it's a wonderful piece of software. I want to get a possibility check on removing some dependencies that might not make much sense to be required in 2024 with the advancements that happened.

CSS in its current state incorporates most of the features that made SASS/SCSS popular – variables and nesting. For me it does not make much sense to use SASS and I think it should not be "forced" as a default. Removing the strict dependency and allowing users to make the decision if they want/need SASS is probably a good idea and doesn't really require much changes for existing sites (adding an entry to the Gemfile) but this could make Jekyll a smaller tool (no need to jekyll-sass-converter, sass-embedded and probably google-protobuf and bigdecimal).

Another dependency that could be made optional is rouge. I bet there's quite a lot of sites built with Jekyll that do not use code syntax highlighting at all.

I could take the task of making these things optional on myself but I want to gather some feedback if this is something that the community and maintainer want.

Resubmitted because I didn't notice the blank issue link and posted as documentation before.

The issue names no files, tests, or entry points. Start by locating the dependency declarations and relevant tests for SASS and Rouge; done means both dependencies can be omitted by sites that do not use them while sites requiring them continue to build, with the behavior covered by tests.