fix(l10n): fixed currency localization for "other than US" locales

[dannycoates]

For en locales that don't have their own ftl file this change
sets their FluentResource to be that of en-GB, which does have
an ftl file in order for the currency to be rendered as 'US$x.xx'
instead of the US fallback of '$x.xx' which is ambiguous in which
currency is meant.

These locales are currently hard coded in AppLocalizationProvider
because other services fail when they can't load l10n files that
are present in supportedLanguages.json but not in the l10n repo.

[chenba]

Appears to be the indirection we want!

[dannycoates]

I tried adding a test to AppLocalizationProvider.test.js but it ends up with no US specifier, i.e. $1.23. It works in a real browser so I wonder if this is a quirk of the test harness? @lmorchard @chenba ideas?

[codecov]

Codecov Report

Merging #5948 into main will decrease coverage by 0.03%.
The diff coverage is 96.69%.

@@            Coverage Diff             @@
##             main    #5948      +/-   ##
==========================================
- Coverage   93.84%   93.81%   -0.04%     
==========================================
  Files         299       58     -241     
  Lines       14417     1551   -12866     
  Branches      385      412      +27     
==========================================
- Hits        13530     1455   -12075     
+ Misses        884       95     -789     
+ Partials        3        1       -2     

Impacted Files	Coverage Δ
...yments-server/src/components/PaymentForm/index.tsx	100.00% <ø> (+1.35%)	⬆️
packages/fxa-payments-server/src/index.tsx	14.03% <ø> (ø)
...ackages/fxa-payments-server/src/lib/AppContext.tsx	80.00% <ø> (ø)
packages/fxa-payments-server/src/lib/apiClient.ts	92.85% <0.00%> (-7.15%)	⬇️
...outes/Subscriptions/Reactivate/ManagementPanel.tsx	100.00% <ø> (ø)
...rver/src/routes/Subscriptions/SubscriptionItem.tsx	90.47% <ø> (-0.44%)	⬇️
packages/fxa-payments-server/src/store/state.ts	100.00% <ø> (ø)
packages/fxa-payments-server/src/App.tsx	65.51% <50.00%> (-1.15%)	⬇️
...erver/src/components/PaymentConfirmation/index.tsx	100.00% <100.00%> (ø)
...ents-server/src/components/PaymentFormV2/index.tsx	100.00% <100.00%> (ø)
... and 242 more

[chenba]

I tried adding a test to AppLocalizationProvider.test.js but it ends up with no US specifier, i.e. $1.23. It works in a real browser so I wonder if this is a quirk of the test harness? @lmorchard @chenba ideas?

Is there a gist or branch I can look at?

[dannycoates]

@chenba https://gist.github.com/dannycoates/b642f757f7f6c52959b66b6e887026bf

[chenba]

Yeah, getLocalizedCurrency still has en-US hard coded for its locale. 😭

[chenba]

In other words, your test is too good. I think we just need to know a string from 'en-GB' is used when the locale is 'en-NZ'?