Major Description
We now have two different implementation for multi-units interval strings to CalendarInterval type values.
One is used to covert interval string literals to CalendarInterval. This approach will re-delegate the interval string to spark parser which handles the string as a `singleInterval` -> `multiUnitsInterval` -> eventually call `IntervalUtils.fromUnitStrings`
The other is used in `Cast`, which eventually calls `IntervalUtils.stringToInterval`. This approach is ~10 times faster than the other.
We should unify these two for better performance and simple logic.