This is Abstract Operation is required for the majority of
InstantConstructor's and InstantPrototype's methods.
The implementation is not entirely complete, (specifically 2 of the
underlying required abstract operations, ParseTemporalTimeZoneString
and ParseISODateTime are missing the required lexing, and as such are
TODO()-ed) but the majority of it is done.
Just like the initial Temporal.TimeZone commit, this patch adds the
Instant object itself, its constructor and prototype (currently empty),
and two required abstract operations.
