Investigate removing Foundation

[dacook]

What we should change and why (this is tech debt)

We have a very old version of Foundation, which is insecure.
It's a big job to upgrade, so maybe the effort is better spent on removing the dependency?

Before making any changes, we want to find out:

• How much of the styles and functionality are relying on Foundation, and
• what would be involved to remove it?

Context

• This came up in chore(deps): bump foundation-sites from 5.5.3 to 6.8.1 #12572