Tracking issue for `Now` namespace

[jasonwilliams]

PR: https://github.com/boa-dev/temporal/pull/70

Upstream issue: https://github.com/unicode-org/icu4x/pull/5081

System info functionality needed:

• [x] SystemTimeZoneIdentifier
• [x] SystemUTCEpochNanoseconds

[nekevss]

So a bit of an update on this. I happened across the tzdb_data crate that we should be able to source Time Zones data. I'm working on adding it to the above PR.

I think that may be the best approach to get a MVP put together sooner rather than later. With a longer term goal of helping ICU4X wherever possible to source from them.

[nekevss]

Now is complete with a functioning version.