utcToZonedTime returns next day when time matches offset

[a1russell]

From #38, which was prematurely closed by its author. Here I'm pasting and editing relevant parts from #38.

The issue appears to exist on Chrome versions 80 and above. Relevant Chrome bug report, which has been closed and marked as WON'T FIX: https://bugs.chromium.org/p/chromium/issues/detail?id=1045791

An example of the problem: https://codepen.io/atomcorp/pen/gObqoyX

In short the following returns a Date object for the 24th not 23rd:

utcToZonedTime(
  new Date('Thu Jan 23 2020 05:00:00 GMT+0000 (Greenwich Mean Time)'),
  'America/New_York' // -5 hours
);

It seems to happen when the inputted time matches the offset of the timezone. So if you move the time of the inputted date an hour back or forward, so it's different to the timezone offset, both utcToZonedTime and the native method return the same.

It's specifically related to do with Intl.DateTimeFormat which is used in tzTokenizeDate.

const dateTime = new Intl.DateTimeFormat('en-US', {
      hour12: false,
      timeZone: 'America/New_York',
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit',
      minute: '2-digit',
      second: '2-digit'
    });

const date = dateTime.format(new Date(2020, 0, 25, 5, 0, 0));

// Chome 79/Firefox etc:  date === 01/25/2020, 00:00:00
// Chrome 81:  date === 01/25/2020, 24:00:00

Example: https://codepen.io/atomcorp/pen/bGNZzZz