Automate L10n extraction locally and in CI

[KevinMind]

Fixes: mozilla/addons#14848

Testing

PR on origin: Link
PR on fork: TBD

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.29%. Comparing base (22435e4) to head (3e764fa).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #12800   +/-   ##
=======================================
  Coverage   98.29%   98.29%           
=======================================
  Files         267      267           
  Lines       10600    10600           
  Branches     3221     3221           
=======================================
  Hits        10419    10419           
  Misses        168      168           
  Partials       13       13           

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[KevinMind]

Generated this PR: #12801

[KevinMind]

I've merged all of the scripts into a single zx executable. It extracts and merges locales for the current code base. It is pretty fast 2x the previous set of scripts (<15seconds locally and in CI)

Local Options

1. Run the locale.mjs script as a pre-commit hook
2. Run the babel plugin directly in our dev and prod builds

CI options

1. Run on every PR, failing if locales are not built
2. Run on pull requests, pre merge (may need queue to do that I'm not sure)
3. Run on master commits, post merge but pre tag
   a. we can commit directly on master
   b. we could open a PR with the generated locale changes.

All options would work, it's more about the kind of experience we want to have.

[eviljeff]

r+wc

[eviljeff]

some of this looks a bit boilerplate-y (e.g. EMAIL@ADDRESS) - does it need updating?

[KevinMind]

Copied verbatim from here. I could actually remove the webpack config file while we are here as that is no longer referenced or needed.