Sass has changed the syntax for dividing two numbers. Previously you
would use `/`, but because this causes some ambiguity with color
functions (`rgb()`, `rgba()`, and the like), where `/` is regularly used
to separate color channel information from an alpha value, Sass has
deprecate the use of `/` for division. [1]
This commit converts all such usages to use `math.div()` instead. This
is a little bit difficult because there are a few places in
`@fortawesome/fontawesome-free` which use the old syntax. There is an
issue open here about it [2] but that has not been fixed yet. So we have
to patch this package to make the deprecation warnings go away.
[1]: https://sass-lang.com/documentation/breaking-changes/slash-div
[2]: https://github.com/FortAwesome/Font-Awesome/issues/18371
