fix(plugin-webpack): keep devDependencies, dependencies, optionalDependencies and peerDependencies in the distributed package.json

[erikian]

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Summarize your changes:

As mentioned in #2818 (comment), the Webpack plugin sets the devDependencies, dependencies, optionalDependencies and peerDependencies objects to {} in the distributed package.json. If any other plugin runs after the Webpack plugin and tries to read one of these objects, it will get an empty object instead of the actual dependencies, which seems like an unexpected side-effect.

Fixes #2818.

[VerteDinde]

@erikian Thanks for the PR (and for your prior PRs, we get excited when we see a submission from you! 😄)

[erikian]

@VerteDinde thanks, glad to hear it!