toHijri in both UAQ and FCNA engines read .year/.month/.day from the
input DateTime — local calendar components — then passed them to
DateTime.utc(). On hosts west of UTC a UTC-midnight local DateTime
resolves to the previous local day, causing toHijri(toGregorian(y,m,d))
to return the wrong Hijri day.
Fix: call date.toUtc() first in both engines before extracting calendar
components. This is symmetric with toGregorian which always returns
DateTime.utc(). Adds 3 regression tests covering the round-trip and the
local-DateTime-on-UTC-west-host case.
