Add webpack-config package

[anomiex]

Changes proposed in this Pull Request:

This is intended to (eventually) take care of several issues in the
monorepo:

• Calypso doesn't use their own calyspo-build webpack config,
  which means it's not likely to be well-maintained.
  • It needs a hack to work with monorepo packages.
  • And another to get correct image paths.
  • And it tries to redefine NODE_ENV, producing warnings.
  • And we have to override a weird default everywhere.
• We have to name our JS files with ".min.js" to avoid their being
  broken by a wpcom minifier, but WordPress.org's translation
  infrastructure ignores such files.
• The plugin used to fix the above had to be forked, adds 772K to
  the plugin, and results in spurious changes in TC builds.
• The way translations are being loaded for lazy-loaded bundles is
  pretty hacky and doesn't lazy-load them.
• We can't use any cache busting for the lazy-loaded bundles, because
  embedding hashes in the filename breaks the link to the translation
  file and putting it in a query parameter breaks building the RTL css.
• Webpack's minification is losing translator comments.
• Calypso-build has a lot of peer dependencies we don't actually need.
  Not everything we have uses sass or postcss, and we have our own
  infrastructure for jest, react, and so on. Currently we just ignore
  the 76 warnings from that.

This is the first step towards fixing that: creating a private package
that can hold the webpack and babel config fragments that we can share
throughout the monorepo. Then we'll have a place to put the fixes for
some of the other issues too.

Jetpack product discussion

PT: p9dueE-3MG-p2

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

No

Testing instructions:

• Does it make sense?

[github-actions]

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[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 D68789-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

[kraftbj]

My internet is acting up and I'm having trouble pushing a resolution commit to get fix the lock file.

Otherwise, looks logical to me.

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D68789-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]

r234325-wpcom