DateTimeFormat: add support for more than two dayPeriod : CLDR's "B" and "b"

[jungshik]

In some locales, they have more than two day periods (AM/PM).

CLDR has data for flexible day periods (B) and 'am, pm, noon, midnight' (b) in addition to "AM/PM" (a). https://www.unicode.org/reports/tr35/tr35-dates.html#dfst-period .

For instance, Chinese (zh) locale data has the following, but there is no way to format time with 'B' or 'b'.

{{{
dayPeriod{
format{
abbreviated{
afternoon1{"中午"}
afternoon2{"下午"}
evening1{"晚上"}
midnight{"午夜"}
morning1{"早上"}
morning2{"上午"}
night1{"凌晨"}
}

....

        availableFormats{
            Bh{"Bh时"}
            Bhm{"Bh:mm"}
            Bhms{"Bh:mm:ss"}
            E{"ccc"}
            EBhm{"EB h:mm"}
            EBhms{"EB h:mm:ss"}

}}}

[jungshik]

@FrankYFTang @littledan @zbraniecki

[jungshik]

@sffc

[FrankYFTang]

I think there are several other time formatting could be improved. Maybe we should put all of that into a proposal instead of dealing with that one by one.

Beside B and b for dayPeriod the other two set are Q/q for quarter and W/w for week

The current skeleton to pattern mapping in locales/zh.txt related to B/b Q/q and W/w

            availableFormats{
                Bh{"Bh时"}
                Bhm{"Bh:mm"}
                Bhms{"Bh:mm:ss"}
                ...
                EBhm{"EBh:mm"}
                EBhms{"EBh:mm:ss"}
                ...
                yQQQ{"y年第Q季度"}
                yQQQQ{"y年第Q季度"}
                yw{
                    other{"Y年第w周"}
                }
            }                                       

in locales/en.txt

            availableFormats{
                Bh{"h B"}
                Bhm{"h:mm B"}
                Bhms{"h:mm:ss B"}
...
                EBhm{"E h:mm B"}
                EBhms{"E h:mm:ss B"}
  ...
                MMMMW{
                    one{"'week' W 'of' MMMM"}
                    other{"'week' W 'of' MMMM"}
                }
...
                yQQQ{"QQQ y"}
                yQQQQ{"QQQQ y"}
                yw{
                    one{"'week' w 'of' Y"}
                    other{"'week' w 'of' Y"}
                }

[FrankYFTang]

I will start a proposal under ECMA402 to extend the DateTimeFormat options

[sffc]

@FrankYFTang Is this issue covered by #346 ?

[FrankYFTang]

@FrankYFTang Is this issue covered by #346 ?

yes