Date time format fix

[estrattonbailey]

DMs were showing as being sent at UTC instead of the user's local time zone on iOS and Android. This seems to have been introduced in #6742.

This new polyfill should allow us to specify a default timezone on app load, but this does not appear to work on iOS or Android. See first commit for that attempt.

In the second commit, I applied the "fix", which is to use the built-in Intl.DateTimeFormat instead of the polyfill. I have not yet confirmed if this regresses #6742.

[github-actions]

Old size	New size	Diff
6.84 MB	6.84 MB	0 B (0.00%)

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[gaearon]

did this in #7196

[surfdude29]

FYI several users in this thread reported times being shown incorrectly, apparently on posts too:

https://bsky.app/profile/pfrazee.com/post/3ldoxeka2uk2y

e.g.:
https://bsky.app/profile/magnolia2010.bsky.social/post/3ldpdxxjwpc2f
https://bsky.app/profile/mdruker.bsky.social/post/3ldpckwazks2s
https://bsky.app/profile/kelsee.bsky.social/post/3ldoxgaxrkk2l

[auroursa]

I faced a timezone issue while exploring #6742. This was my solution at the time (I hope this helps). Since no longer relied on datetimeformat to output time, I thought it was no longer an issue and removed it. I sincerely apologize for the consequences of not testing it thoroughly.

[auroursa]

Upon rechecking the first commit, it seems that it was just missing import '@formatjs/intl-datetimeformat/add-all-tz.js', adding it will make it work properly.

[auroursa]

According to the first commit, the missing import has been added. Please see #7204.