moment.utc(date).tz(timezone, true) incorrect date around DST days

[arturzealves]

Moment-timezone version which you use:

Version: 0.5.33

Issue description:

Australia/Sydney changes its time on 2020-04-04 at 03:00:00, moving backward to 02:00:00
moment-timezone has an issue parsing a date from UTC to Australia/Sydney (with Boolean = true) on the day before Daylight Saving Time Ends:

  - moment.tz('2021-04-03 15:00:00', 'Australia/Sydney');
  Moment<2021-04-03T15:00:00+11:00> // Correct
  
  - moment.tz('2021-04-03 15:00:00', 'Australia/Sydney').toISOString();
  '2021-04-03T04:00:00.000Z' // Correct
  
  - moment.utc('2021-04-03T15:00:00.000Z').tz('Australia/Sydney', true);
  Moment<2021-04-03T15:00:00+11:00> // Correct
  
  - moment.utc('2021-04-03T15:00:00.000Z').tz('Australia/Sydney', true).toISOString();
  '2021-04-03T04:00:00.000Z' // Correct

But:

  - moment.tz('2021-04-03 16:00:00', 'Australia/Sydney');
  Moment<2021-04-03T16:00:00+11:00> // Correct

  - moment.tz('2021-04-03 16:00:00', 'Australia/Sydney').toISOString();
  '2021-04-03T05:00:00.000Z' // Correct

  - moment.utc('2021-04-03T16:00:00.000Z').tz('Australia/Sydney', true);
  Moment<2021-04-03T16:00:00+10:00> // Incorrect

  - moment.utc('2021-04-03T16:00:00.000Z').tz('Australia/Sydney', true).toISOString();
  '2021-04-03T06:00:00.000Z' // Incorrect

[gilmoreorless]

From what I can tell, moment-timezone is first grabbing the UTC offset for the Australia/Sydney zone for the existing timestamp, then storing the inverted result as the internal offset calculation.

This works fine most of the time, but in the case you've found, it means Sydney's offset for 2021-04-03 16:00 UTC is being used (which is +10:00), instead of the correct offset for 2021-04-03 16:00 Sydney (which is +11:00).

[adityapachpor978478]

epoch 1678615200000 is actually Sunday March 12, 2023 03:00:00 (am) in time zone America/Los Angeles (PDT) but moment results in "Sun, Mar 12 2023 - 02:00"
https://www.epochconverter.com/timezones?q=1678615200&tz=America%2FLos_Angeles
https://jsfiddle.net/adityapachpor/abqsmu40/

Is this the same issue as yours?