storybook: Use webpack 5 everywhere

[anomiex]

Changes proposed in this Pull Request:

They refactored everything to use either 4 or 5, but left a lot of
webpack 4 deps in various subpackages. Either unused, or using
functionality that wasn't changed between 4 and 5.

This PR adds overrides to force webpack 5 in place of 4. That removes a
bunch of webpack 4 deps on chokidar 2, which is itself deprecated and
depends on a version of glob-parent that pnpm audit complains about.

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Is the build happy?
• Does the storybook code in the build artifact look good?

[github-actions]

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[jeherve]

Does the storybook code in the build artifact look good?

This seems to look good, no issues there!

This is going to need a rebase though.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello anomiex! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D66187-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D66187-code, and commit it.
Once you've done so, come back to this PR and add a comment with your changeset ID.

Thank you!

[anomiex]

r231161-wpcom