Fix: Advanced format output with short offset name

[klm-turing]

• Used of long timezone name by default in Intl.DateTimeFormat
• Extract and cached short offset name from the long one in the offsetName function
• Writing related unit test

This fix 1713 issue

[et]

Thanks for adding this! I definitely could use this in a moment migration. @iamkun - curious if we can get this in?

Alternatively, have we considered replicating moment-timezone's zoneAbbr functionality? https://momentjs.com/timezone/docs/#/using-timezones/formatting/