Font-Display check should consider icon fonts

**Feature request summary**
A special check to not recommend `font-display: swap` for icon fonts.

**What is the motivation or use case for changing this?**

There seems to be no clear recommendation on what is actually best practice for icon fonts, and even if there is, it's not `swap` but actually `block`. So I would suggest either adding a special rule to to detect icon fonts or maybe whitelist the most common ones so they don't trigger the lighthouse warning when `swap` is not set.

Relevant links:
- https://github.com/FortAwesome/Font-Awesome/issues/14387
- https://www.zachleat.com/web/font-display-icon-fonts/
- https://stackoverflow.com/questions/49461308/correct-font-display-value-for-icon-fonts

**How is this beneficial to Lighthouse?**

Currently the Lighthouse recommendation is not actual the best practice and might cause people blindly following it to get unintended behaviour.