[dev] strftime deprecation

[Ralf Lang]

Hello,

I am thinking about the correct way to replace strftime calls in our 
codebase.
The strftime function is deprecated.

It is aware of the currently set locale and uses a different way of 
templating date strings than DateTimeInterface::format or 
IntlDateFormatter::setPattern||

https://www.php.net/manual/de/intldateformatter.format.php
https://www.php.net/manual/de/datetime.format.php

In some places, date formats are defined by Horde's prefs

date_format
date_format_mini
time_format
time_format_mini

These settings are encoded in strftime mask formats and there are the 
placeholders %X and %x to represent the locale's preferred date and time 
settings.

There are three possible routes.

- Not deal with the issue now. Notices will be emitted and by PHP 9 this 
will eventually break.
- Keep the prefs format and build a helper that adapts strftime-like 
format strings to their DateTime equivalents.
- Change the actual prefs values to native DateTime formats. Requires 
additional effort to upgrade existing pref data. Cleanest solution though.


Regards


Ralf