Respect user preferences when formatting timestamp (#7994)

This is a follow up to #7945. The current behaviour reads the locale and
infers from that which type of time format should be used (12 hour/24
hour).
However, in macOS you can override this behaviour, e.g. you can use
en_US locale but still use the 24 hour clock format (Can be customized
under Settings > General > Date & Format > 24-hour time). You can even
customize the date format.

This PR uses the macOS specific `CFDateFormatter` API, which outputs
time format strings, that respect those settings.

Partially fixes #7956 (as its not implemented for linux)

Release Notes:

- Added localization support for all macOS specific date and time
configurations in chat