chore: update karma-webpack to v5.0.1, adapt tests

[pichlermarc]

Which problem is this PR solving?

We've been using karma-webpack@4 which is not compatible with webpack@5 that we were using since #4340
Since webpack 5, node polyfills are not automatically included anymore, so we have to add polyfills manually.

Using an old verison of karma-webpack with a new version of webpack may be is what's causing test failures in #4622, as one can't access any other entrypoint than @opentelemetry/api

Notable changes:

• we use assert in our tests, so I included the assert polyfill
  • the assert polyfill needs the util polyfill, so I included that
    • the util polyfill needs a process polyfill, so I included that too

Requires #4649
Supersedes #4647, tests fail as no polyfills are added.
Enables #4622, where we can't import @opentelemetry/api/experimental in browser tests unless we update karma-webpack

Type of change

• internal for the test changes

[pichlermarc]

Well that's no fun. Looks like karma-webpack is not working on macOS. #2234

[pichlermarc]

Well that's no fun. Looks like karma-webpack is not working on macOS. #2234

Actually it looks like this is working, I asked @dyladan to run it on his mac and it works there.

I'll wait for #4649 until marking this as ready for review 🙂
If any other macOS users stumble upon this please try to run the browser tests locally and let me know if you experience any problems.

[pichlermarc]

needed so that we mock the right thing for the right platform, process is now defined due to the required polyfill, so we're using process?.versions?.node instead to determine if we're running in Node.js or the browser.

[trentm]

If any other macOS users stumble upon this please try to run the browser tests locally and let me know if you experience any problems.

Tests passed for me locally on macOS using Node.js v20.12.2.