getFormatDateInfo should say if pattern is a date or not

[borgar]

Ideally, the output structure should emit a type field to show if pattern is really a date or not. Something like this:

type FormatDateInfo = {
  // new date type field
  type: "date" | "time" | "datetime" | "none",
  clockType: 12 | 24,
  seconds: boolean,
  minutes: boolean,
  hours: boolean,
  day: boolean,
  month: boolean,
  year: boolean,
}

This has the benefit that:

1. You don't have to call isDateFormat to determine if something is a date beforehand.
2. You can pass the info.time into a map of default patterns:

const ISO_PATTERNS = {
  date: "yyyy-mm-dd",
  time: "hh:mm:ss",
  datetime: "yyyy-mm-ddThh:mm:ss",
  none: "General",
};

// return an ISO formatted date, or a general formatted number, based on a cell format pattern:
const info = getFormatDateInfo(pattern);
const normalizedPattern = ISO_PATTERNS[info.type];
return format(normalizedPattern, value);

---

Alternatively, we might consider a isDate + granularity approach:

type FormatDateInfo = {
  // new "is a date or not" field
  date: boolean,
  // new granularity field
  granularity: "year" | "month" | "day" | "hours" | "minutes" | "seconds" | "none",
  ...
}

This does make it impossible to differentiate the "time" type though, so maybe it makes sense to do both.