Unordered interval units

Currently, Spark requires particular order of interval units in casting from strings - `YEAR` .. `MICROSECOND`. PostgreSQL allows any order:

maxim=# select interval '1 second 2 hours';
 interval
----------
 02:00:01
(1 row)

but Spark fails on while parsing:

spark-sql> select interval '1 second 2 hours';
NULL