Consider Adding Specific Formatter for Long Formatting in for currency formatter

[younies]

Consider Adding Specific Formatter for Long Formatting in for currency formatter

[robertbastian]

This would keep the data split between the short&narrow and long formatters.

Splitting data doesn't require a different type. If the data for short, narrow, and long, has the same shape, it should use the same data struct, just with three different markers and three different constructors.

[sffc]

• @robertbastian Are the shapes of the data the same?
• @sffc The shape is different from short/narrow currency, but is it the same as units?
• @younies:
  • in currencies:
    • pattern-one: "{0} {1}" per locale
    • display-name-one: "us dollar"
  • in units:
    • meter-pattern-one: "{0} meter" per unit
• @sffc You could merge them at datagen time? "dollars per mile"
• @younies There are a lot of open questions. Will users give units like: usd-per-meter
• @sffc OK, so the pattern should be in its own marker, or currency essentials. And the names should go into a marker called "long currency".
• @robertbastian In isolation this makes sense, but I don't know if it makes sense in the context of icu_dimension.
• @sffc Currency is being designed as a standalone formatter.
• @robertbastian The APIs should be similar to each other.
• @younies Units are different. You construct complex units, use the unit identifier parser, maybe perform conversion, etc. With currency, people just give the currency code and that's it.

Data markers:

• CurrencyEssentialsV1
• CurrencyLongEssentialsV1
• CurrencyLongNamesV1

Formatters:

• CurrencyFormatter
  • Bikeshed: ShortNarrowCurrencyFormatter?
• LongCurrencyFormatter

LGTM: @sffc @younies