React 18/webpack 5 follow up

[kmcfaul]

Notes about the dependency upgrades and things to potentially follow up on from #3454.

• Replace @reach/router (and current workaround @gatsbyjs/reach-router) with React's router. Reach has a built in older version of React that isn't playing nice with 18.
• Remove file-loader dependency (isn't used anymore)
• Investigate path-browserify and process usage to see if they are necessary (there should be a better way of getting path and process environment variables). Used in scripts/webpack/webpack.base.config.
• Convert cli scripts to typescript for better intellisense/error logging
• In scripts/cli/start.js, investigate new syntax for enabling error logging
• In scripts/webpack/webpack.client.config, investigate what the replacement for the deprecated stats prop is, and look up compress and why the recommended default is true.
• In scripts/webpack/webpack.server.config, investigate null loader usage that was removed for nonvc (we may need an alternative, but the build is currently working without it)
• Revisit Monaco usage (React issue is already open?)
• Double check asset/resource usage (this replaced the various loader modules) but it looks to be working atm
• Validate CSS loading (that we aren't loading it multiple times)
• Investigate webpack's included Terser plugin and its usage
• Investigate caching and cleaning for the build process - you shouldn't need a yarn clean between builds but the clean isn't properly emptying all the caches
• Investigate removing node SSL legacy option from the start script