chore(payments): upgrade @fluent/bundle et al.

[stasm]

Because

• Fluent packages used to ship two build artifacts: index.js written in the most current ES version, and compat.js transpiled to ES2017. In Remove compat.js build artifacts projectfluent/fluent.js#472 we removed the compat.js builds and set tsc to target ES2018.
• I didn't think it was appropriate for upstream Fluent to make the decision about the browsers supported by the compat.js builds. It's something that app developers should have more control over.
• The expectation is that apps using Fluent will be able to transpile node_modules dependencies to match their browser compatibility requirements.

This pull request

• Is based on chore(payments): upgrade to @fluent/react 0.12.0 #6096. Only the last commit is new compared to chore(payments): upgrade to @fluent/react 0.12.0 #6096
• Upgrades three @fluent packages used by payments-server: @fluent/bundle, @fluent/react, @fluent/langneg to their newest versions which ship ES2018 code.
• As far as I was able to verify it, the files built with yarn build in build/static/js are transpiled by FxA's build system correctly to match your browerlist config.

Checklist

Put an x in the boxes that apply

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).

[stasm]

Other than transpilation, it's worth to mention that Fluent uses fairly new methods like Object.entries(), Array.prototype.includes(), and String.prototype.includes(). Looking at https://github.com/mozilla/fxa/blob/main/docs/supported-browsers.md I think all target browsers should support them. Do you run any cross-browser integration tests to ensure compatibility?

[codecov]

Codecov Report

Merging #6098 into main will increase coverage by 1.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6098      +/-   ##
==========================================
+ Coverage   93.84%   94.86%   +1.01%     
==========================================
  Files         299       59     -240     
  Lines       14417     1656   -12761     
  Branches      385      453      +68     
==========================================
- Hits        13530     1571   -11959     
+ Misses        884       84     -800     
+ Partials        3        1       -2     

Impacted Files	Coverage Δ
packages/fxa-payments-server/src/App.tsx	100.00% <ø> (+33.33%)	⬆️
...payments-server/src/components/AppLayout/index.tsx	93.75% <ø> (ø)
...erver/src/components/PaymentConfirmation/index.tsx	100.00% <ø> (ø)
...yments-server/src/components/PaymentForm/index.tsx	100.00% <ø> (+1.35%)	⬆️
...ents-server/src/components/PaymentFormV2/index.tsx	100.00% <ø> (ø)
...-server/src/components/PaymentLegalBlurb/index.tsx	100.00% <ø> (ø)
...yments-server/src/components/PlanDetails/index.tsx	96.77% <ø> (+0.34%)	⬆️
...ts-server/src/components/TermsAndPrivacy/index.tsx	100.00% <ø> (ø)
...xa-payments-server/src/components/fields/index.tsx	99.04% <ø> (-0.03%)	⬇️
packages/fxa-payments-server/src/index.tsx	14.03% <ø> (ø)
... and 251 more

[chenba]

Let's rebase main once #6152 is merged to see if these conflicts will go away.

[chenba]

Closing in favor of #6291.