Updated icu4x deps to 2.x

[bim9262]

icu_locid has been replaced with icu_locale_core.
Removed direct dependency on icu_calendar.
Added precision argument to datetime formatter to specify the precision of the datetime.

[bim9262]

Any thoughts on having an argument on the datetime formatter that's only accepted when using ICU datetimes?

[bim9262]

@ammgws
Any thoughts on having an argument on the datetime formatter that's only accepted when using ICU datetimes?

[bim9262]

Separated the icu4x version 2 update from the added precession argument.