Read the distance of times as the interval MEOS answers

[estebanzimanyi]

tstzspan.distance answers the seconds, with their fraction, of the interval
distance_tstzspan_tstzspan and distance_tstzspanset_tstzspan return, and tstzset.distance
the Duration of the interval distance_set_timestamptz and distance_tstzset_tstzset return.
ConversionUtils.interval_to_timedelta reads an interval's fields where the catalog lays them
out, the microseconds at byte 0, the days at byte 8 and the months at byte 12, and refuses an
interval holding months, which has no fixed duration. ConversionUtilsIntervalTest reads one
day, a time below a day, a fraction of a second and days with a time, and refuses one month;
TsTzSetTest asserts the 120 days between its sets.

Witness: MobilityDB 43cfd3f936 (#2942) returns the seven distances between times as an
Interval *, where they returned a double, and jmeos-core no longer compiles against it:
tstzspan.java and tstzset.java pass the Pointer where a double is read. interval_to_timedelta
parsed interval_out with a pattern of "N days HH:MM:SS", so "1 day", "03:04:05" and
"00:00:01.25" raised or lost their fraction.

Why: JMEOS builds against MobilityDB master, so every JMEOS build fails until it reads the
interval MEOS answers.

Measured: against MobilityDB 43cfd3f936 and the catalog of MEOS-API 1192ae4f01, the clean
build and suite pass, 1,800 and 106 tests, with no warning.