Unfortunately, this reverts back some changes made in #1982 that had to be made as an Uncaught ReferenceError: FontAwesome is not defined error appears, which prevents custom icons from being added (see screenshot where these are missing from our navbar)

There are for sure improvements needed on how we handle FA, which also result in what you see in #2115, so merging this PR would directly impact any users adding custom icons to their documentation, so I would prefer not merging this PR and instead going back and properly fix the FA vendoring (using SVG only vs the current SVG + webfont approach, but that would also need extra work on components like admonitions and what not to ensure proper rendering), I just have not had enough bandwidth to focus on that larger piece of work.