Add support for the Quarters field "Q"

[gregtatum]

As a follow-up to #481, we need support for the "Q" field, which is Quarters.

[sffc]

Discussion on quarters, from email chain followed by discussion on 2021-02-12:

@sffc:

UTS 35 defines a "quarter" as the 'Q' field, but the definition of a quarter is not transferable to all locales, domains, and calendar systems (https://github.com/tc39/ecma402/pull/345). For example, some locales and regions use trimesters, tropical seasons, sidereal seasons, and other mechanisms in the way that en-US uses quarters. Therefore, would you consider it acceptable for ICU4X to consider the formatting of quarters to be out of scope?

@pedberg-icu:

I have not personally seen formats with Q used much if at all in the Apple software that I work with. I think the need for formats with Q was primarily driven by companies that needed to do business planning and financial reports. You would probably get a better answer about this from people at a company like TurboTax, or perhaps people who work on Google Calendar or perhaps on some business planning software. I think it is likely to be useful for them (even if the concept of quarters does not make otherwise make sense within a given cultural context, it may be a useful external concept when coordinating multinational business activities).

@sffc:

I recommend following ECMA-402 on this one and do not include quarters in ICU4X DateTimeFormat data. Wait for a client like TurboTax to come to us and ask for us to add support in the future.

Thumbs-ups from: @mihnita, @gregtatum, @dminor, @Manishearth

[blaynem]

Hey, Workday might qualify for this!

We're looking to do something similar to: https://icu4j-demos.unicode.org/icu4jweb/flexTest.jsp?pat=QQQQyyyy&_=en

Where we can supply a date and width of the quarter to display as.