chore: upgrade webpack-dev-server and other dev deps

[adidahiya]

Changes proposed in this pull request:

Upgrade various dev dependencies, including some major version bumps:

• https://github.com/postcss/postcss-cli/blob/master/CHANGELOG.md#1000--2022-06-29
• https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md#700-2022-05-18
• https://github.com/webpack-contrib/source-map-loader/blob/master/CHANGELOG.md#400-2022-06-13
• https://github.com/mochajs/mocha/blob/master/CHANGELOG.md#1000--2022-05-01
• https://github.com/webpack-contrib/copy-webpack-plugin/blob/master/CHANGELOG.md#1100-2022-05-17
• https://github.com/scinos/yarn-deduplicate/blob/master/CHANGELOG.md#600---2022-08-29
• https://github.com/sinonjs/sinon/blob/main/docs/changelog.md#1400
• https://github.com/webpack/webpack-dev-server/blob/master/migration-v4.md
• https://github.com/webpack/webpack-cli/blob/master/packages/webpack-cli/CHANGELOG.md

Most notable is the webpack-dev-server upgrade, which required a migration of the webpack config. We probably want to major version bump for this change.

[blueprint-bot]

upgrade webpack-cli and webpack-dev-server

Previews: documentation | landing | table | demo