Switch bundler from ESBuild to Webpack

[koesie10]

In terms of keeping down the number of dependencies and different tools we are using, this switches the bundler for the main extension module from ESBuild to Webpack to keep it in line with the bundler used for the webview.

⚠️ This is based on #1799 and is just for testing whether this also works (for now).

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[koesie10]

For now, let's see how well ESBuild works. If we run into any problems or want to unify the two builds, we can think about switching this to Webpack.