Implement `resolve_components` for `ZonedDateTimeFormatter`

[jedel1043]

The purpose of #1361 was to easily obtain the resolved options of a DateTimeFormatter for ECMA-402 implementations. Unfortunately, the DateTimeFormat service requires a ZonedDateTimeFormatter instead, and said component doesn't have an equivalent method to obtain its resolved options.

[sffc]

@jedel1043 The support for datetime components is experimental; there is a fairly clear path forward to bring them to a point where we can launch them as stable. Would you be interested in contributing to ICU4X to bring datetime components to the finish line? Happy to jump on a call to discuss.

[jedel1043]

@sffc I'd love to! Would need some guidance though, since I'm still getting accustomed to the repo 😅

[sffc]

@jedel1043 Cool! Can you message me, sffc at google dot com, to set up some time?

[sffc]

@jedel1043 I'm assigning this to you since it is related to the components bag work.