migrate babel to swc

[hkennyv]

NextJS 12+ now uses swc for js transpilation. Although it still supports using babel (and will automatically opt-out of swc if it detects a .babelrc, it would be nice to keep up-to-date.

So far, we only use babel for the following plugins:

• babel-plugin-prismjs

Once the above works with swc, we can drop babel.