feat: usercss

[lewisakura]

Full UserCSS support for Vencord, featuring a settings dialogue, compilers for stylesheets (LESS and Stylus supported), and hot-reload (both for variable changes and when the stylesheet code is updated).

[lewisakura]

TODO:

• settings UI
• storing usercss settings somewhere

WONTFIX:

• conflicting variable names (this will usually result from using two large themes at once which is a very silly idea, and snippets should really be using unique variable names unless they're doing the same thing)

[lewisakura]

I have written some tests that demo all of the compilers and some error resiliency in case you want to try it out. If your text goes red, it did the thing.

[lewisakura]

i'm so tired

[lewisakura]

As far as I'm concerned, the actual feature implementation is now complete, so it's just refactoring and cleanup. I'll open it for review for suggestions on the aforementioned.

[lewisakura]

conflicting variable names (this will usually result from using two large themes at once which is a very silly idea, and snippets should really be using unique variable names unless they're doing the same thing)

This is not really the case and I sort of "fixed" it by isolating UserCSS variable configuration into their own settings subsets. In the case of vanilla CSS though (where it's injected using a :root selector) this can still cause conflicts, but in other compiled themes (i.e., Less, Stylus, and USO) it will work without conflict.

[wolfieboy09]

This has not been merged yet @coolesding