This AO is required for a bunch of PlainTime related methods.
As part of this change the `TemporalTime` record was renamed to
`UnregulatedTemporalTime` and a new `TemporalTime` record that matches
the other Temporal parse result records was added. This also has the
added benefit of getting rid of a would be round-trip cast from integer
to double and back in `ParseTemporalTimeString`.
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.