Should serializing a FixedOffsetTimeZone like `TimeZone.UTC` just yield a `'Z'`? This was violating ...

# kotlinx-datetime

[kevin.cianfarini]

Should serializing a FixedOffsetTimeZone like TimeZone.UTC just yield a 'Z'? This was violating a backend contract we have and took me by surprise. Doing TimeZone.of("UTC") fixed this.

[kevin.cianfarini]

I believe the tzdb name should be Zulu during serialization.