upgrade Webpack to v5, convert config files to ESM

[derhuerst]

As proposed in HSLdevcom#4756, this PR intends to bring the tooling up-to-date:

• upgrade Webpack to ^5
• converts config files from CommonJS to ES Modules (ESM)
• removes the -r esm helper from digitransit-{component, search-util,util,store}/*/package.json
• all changes from Yarn v3 #22, which includes changes of chore: upgrade to node16 #21

Still to do:

• confirm that everything works
• finish adapting webpack.config.babel.js to Webpack 5