[translations] Try SWC plugin for lingui, remove babel

[Atmosfearful]

New lingui swc-plugin https://github.com/lingui/swc-plugin

SWC should give us faster builds. https://nextjs.org/docs/advanced-features/compiler#why-swc

Preliminary research

• aside from lingui, what else needs babel? Can we remove @emotion/babel-plugin?

Todos

• npm install the lingui swc plugin it for app and site
• Using the swcPlugins field in next.config.js update config to use the swc lingui plugin for app and site
• delete babel config and any other babel stuff
• see if the builds are faster and document the difference in speed (I can provide vercel access to view builds)

[biwano]

@Atmosfearful If we are still doing this, I need to add the code to carbonmark too.

[Atmosfearful]

This was tested here #927
But no significant speedup was detected so we will stick with the tried-and-tested babel builds