Accept strings or util.TimeZone instances

[thekid]

Following the paradigm: Be liberal in what you accept, all of these methods now accept ?string|util.TimeZone instead of just ?TimeZone:

• util.Date's constructor
• util.Date::now()
• util.Date::create(...)
• The format() method
• In toString()

[thekid]

Released in https://github.com/xp-framework/core/releases/tag/v12.2.0