Upgrading to webpack-config v4

Ensure webpack is at least v5.
Ensure webpack-cli is at least v4.
Replace webpack --env.production with webpack --env production.
Replace webpack-dev-server --open with webpack serve --open.
Migrate to ESM (preferred), or use a "-commonjs" config to continue using CommonJS.

Migrating to ESM

Set type: "module" in package.json
Rename webpack.config.js to webpack.config.cjs
Change all import ... from "foo" to foo.js (even if the source file is .ts or .tsx).
Change all import foo = require("foo") to import foo from "foo.js" (even if the source file is .ts or .tsx).
Migrate AVA to ESM if required (see https://github.com/avajs/ava/blob/main/docs/recipes/typescript.md#for-packages-with-type-module)
See https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c for further advice on ESM migration.