Formatting of relative and absolute dates using Intl.* APIs

[niik]

Closes #13943

Description

This adds region-aware formatting for relative and absolute dates using the Intl namespace. This builds on #14149, #14123 and app.getLocaleCountryCode

Note that this is not about localizing strings, the interface will remain US-english, it will however apply the correct (hopefully) regional settings for formatting numbers. Most notably right now this means that users like myself who have their OS configured to display 24-hour format will now.

Note that this is feature-flagged and currently only enabled for dev.

cc @tsvetilian-ty as author of #13965

Screenshots

For reference these are my regional settings on Windows and macOS (they resolve to en-SE on both platforms)

Release notes

Notes:

[sergiou87]

Everything is terrible

:its-true-all-of-it:

[niik]

@sergiou87 Merge conflict, need a little ✅ again please

[sergiou87]

As discussed in Slack, it's not picking the 24h format for me, but seems to be an issue with Intl rather than with your implementation:

[niik]

Alright, after significant investigation here we've determined that we're not quite ready to jump on the regional-aware train just yet. There are some notable en-* locales that isn't defined in the Unicode Common Locale Data Repository such as en-ES, en-NO, en-FR, etc.

We have ideas for how to address this though and in the meantime we'll be using the en-US-POSIX locale by default. The POSIX variant of en-US is essentially US-english but without number grouping (i.e it's essentially .toString()).

Given the recent discoveries I'm moving the feature flag back to dev and intend to tackle the locale resolution in a separate PR.

@sergiou87 Another look when you've got time please?

[sergiou87]

Looks and works good!