[react-i18n] Fix unformatCurrency utility stripping significant digits on RSD currency

[lhoffbeck]

Description

Part of a fix to resolves Shopify/shopify issue #284738, along with shopify/web PR #43731.

RSD supports 2 decimal places, but (per Christian Jaekl)

...they've become worthless and fallen out of use. (1 para ~= $0.0001 USD currently, so 1RSD is approximately 1 US cent). ... Stripe still considers RSD to have subunits. In Chrome, Intl.NumberFormat treats RSD as if it has no decimals, which is what you're getting if you call formatCurrency without a form: parameter.

For example:

new Intl.NumberFormat('en-CA', {style: 'currency', currency: 'RSD'}).format('1.55')
	-> "RSD 2"
new Intl.NumberFormat('en-CA', {style: 'currency', currency: 'CAD', form: 'short}).format('1')
	-> "$1.55"

Because of this, when our unformatCurrency utility calls currencyDecimalSymbol, the formatCurrency rounds all RSD values to the nearest Int--unless you pass a form: short.

This change adds the form: short option to the currencyDecimalSymbol utility and updates the tests to check for this use case.

To 🎩 you can remove the change and the RSD test should fail.

Type of change

• react-i18n Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above (Documentation fix and Test update does not need a changelog as we do not publish new version)

[atesgoral]

Suggested change

	## Unreleased
	- Fixed `currencyDecimalSymbol` function returning `DECIMAL_NOT_SUPPORTED` for RSD
	<!-- Unreleased -->
	- Fixed `currencyDecimalSymbol` function returning `DECIMAL_NOT_SUPPORTED` for RSD [#1902](https://github.com/Shopify/quilt/pull/1902)

[lhoffbeck]

saw this just after I pushed the change up 🙈

[atesgoral]

There's more to update though :) The heading is a comment, and we recursively mention the PR

[lhoffbeck]

ahh will fix :)

[atesgoral]

@lhoffbeck @shopify/react-i18n@5.3.8 is released