SCSS variables output

[timhettler]

This PR riffs off the CSS variable output feature to enable SCSS variable output. A few important distinctions:

1. Filenames have a leading underscore (_) to follow Sass's partial convention.
2. SCSS variables are not prefixed with the frame name as I did in Prefix CSS variables with frame name #203; this is because Sass has it's own namespace convention to avoid global variable collisions, e.g:

@use "./tokens/colors";
@use "./tokens/borderWidths";
@use "./tokens/fontFamilies";

button {
 color: colors.$green3;
 border: 1px solid borderWidths.$regular;
 font-family: fontFamilies.$regular;
}

[mikaelvesavuori]

Hi again @timhettler! A great addition to Figmagic. Seems you covered all of the bases - happy to merge!

[mikaelvesavuori]

Wonderful work! 🚀 Now released in https://github.com/mikaelvesavuori/figmagic/releases/tag/v4.5.14