front: cleanup date helpers

[emersion]

Description and goal

We have a bunch of helpers in utils/date and utils/timeManipulation. Some of these are buggy, some could improved to be more type-safe, some are overlapping in functionality, and they all could be tweaked to be more consistent.

I've been working on this for a while already, this issue is about the remaining work.

utils/date

• timestampToHHMMSS(): can be replaced by dateToHHMMSS(), which is more type-safe (front: improve OperationalPointWithTimeAndSpeed type safety, drop timestampToHHMMSS() #10876)
• formatIsoDate(): should be replaced with something working with local dates
• Revamp/unify date formatting utils:
  • dateTimeFormatting()
  • formatDay()
  • formatDateToString() and extractDateAndTime()
  • serializeDateTimeWithoutYear()
  • formatDateString()
  • dateToHHMMSS()
  • dateToDDMMYYYY()
  • formatToIsoDate() (front: drop formatToIsoDate() #10845)
• formatLocaleDateToIsoDate(): should be dropped, replaced by Date.toISOString()
• isoDateToMs(): should be dropped (front: drop formatToIsoDate() #10845)
• isoDateWithTimezoneToSec(): should be dropped
• formatDateForInput(): should be replaced with something similar to formatLocalDateTime()
• convertUTCDateToLocalDate(): should be dropped
• generateISODateFromDateTime(): needs investigation? (mutates input arg, awkward API)
• formatLocaleDate(): should be dropped, buggy (front: fix isEqualDate() #10846)
• formatTimeDifference(): should be moved to Duration?

utils/timeManipulation

• sec2ms(), ms2sec(), minToMs(), durationInSeconds(), calculateTimeDifferenceInDays(), secToMin(), SECONDS_IN_A_DAY: should be replaced by Duration
• datetime2time(), time2datetime(), sec2datetime(), secToHoursString(): weird to use d3 for this, overlaps with time formatting helpers from utils/date? (front: drop TimeButtons, TrainDetails and ChartSynchronizer #10881)
• sec2time(): uses UTC instead of local time?

Acceptance criteria

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