build(webpack-dev-server): fix examples by rolling back webpack-dev-server version

[sankhesh]

Rolled back to v4.9.0

Context

Updating webpack-dev-server in 3953b55 to v5.2.2 caused the incompatibility with parallel-webpack and had the following issue:

[webpack-cli] Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.
 - options has an unknown property '_assetEmittingPreviousFiles'. These properties are valid:
   object { allowedHosts?, bonjour?, client?, compress?, devMiddleware?, headers?, historyApiFallback?, host?, hot?, ipc?, liveReload?, onListening?, open?, port?, proxy?, server?, app?, setupExitSignals?, setupMiddlewares?, static?, watchFiles?, webSocketServer? }

Related: #3313 (comment)

Results

Changes

• Documentation and TypeScript definitions were updated to match those changes

PR and Code Checklist

• semantic-release commit messages
• Run npm run reformat to have correctly formatted code

Testing

• This change adds or fixes unit tests
• Tested environment:
  • vtk.js:
  • OS:
  • Browser:

[jourdain]

It has been too long, I let Julien take the lead on that one.

[finetjul]

It does not seem future-proof however... but if you can still do npm run example AnExampleHere from a fresh build, then I guess it's fine by me.

[github-actions]

🎉 This PR is included in version 34.12.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• GitHub release

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