fix: importing the project using modern CSS loaders

[tymees]

I encountered an issue with more modern CSS loaders, in which importing from node_modules breaks completely. Instead, those expect that you import stuff as-if you're already in node_modules (effectively, that's what is happening...)

This PR changes the repo to remove all 'imports from node_modules', and makes sure the build process still works by emulating what those CSS loaders do.

EDIT: as a bonus, I included a fix for the GitHub actions workflow. The step versions used were too old. Technically, this should be a different PR, but I hope you don't mind it being included here?

[XanderVertegaal]

(100% fine with updating the build workflow in this PR, no worries.)

The changes themselves are fine, but I'm getting a million deprecation warnings when running the docs project. A few are simple typos (which can be ignored for now); others are deprecation warnings from Bootstrap, which we cannot solve (twbs/bootstrap#41512).

You can silence the latter by updating nuxt.config.ts:

    vite: {
        ...
        css: {
            ...
            preprocessorOptions: {
                scss: {
                    quietDeps: true,
                },
            },
        },
    },

You then see a few warnings that are genuinely from this project; I saw these pop up in VueLib as well. They are mostly about @import being replaced by @use and global built-in functions being deprecated.

You might want to address those in this PR as well since they seem to be linked to the SASS loader, but if you don't think they're a problem, that is fine too. Let me know in that case.

[tymees]

No, those deprecation warnings are 100% caused by Bootstrap. See also this issue:
twbs/bootstrap#40962

And even if Bootstrap had already migrated to @use, that migration isn't a simple thing. So, I'd rather not do that as part of this PR

[XanderVertegaal]

Right, no problem :)

[mrholek]

We migrated our Bootstrap fork completely to Sass modules; you can see how to do it here - https://github.com/coreui/coreui