SASS support

[Leinnan]

There is already existing crate that would allow really easy to add support for SASS extension to CSS.
I have example implementation of the feature: Leinnan@346ced7

[Leinnan]

I think once this is live, that change could be an easy one to do and be separated behind a feature that could be disabled by default:
bevyengine/bevy#10565

[afonsolage]

I'm not experienced with SASS, but if at the end grass converts into a regular css content, then yeah, this would be done with Asset Preprocessor (.sass -> .css);

[afonsolage]

I forgot to say, but I'll take a look into SASS, create an example and check if we could use Asset Preprocessor