Upgrade to React 18.2.0

[aminomancer]

Maybe depends on #191.

I did some testing and everything seems to compile correctly on React 18.2 now. And we want to, because in order to start parsing the TS in content/ correctly, we need to get the typings sorted. And we're currently using react-select whose types depend on React types that don't exist in React 16.12 (what we're using now). Which only works because type checking isn't correctly set up for content.

This will help in upgrading to parcel v2 (#211), which means abandoning tsc and fixing a whole load of little incompatibilities, changing our CSS module system, ditching CJS.