Added tests for aliases and various calendar properties, ensured
dateToJulianDay()'s invalid date branch is exercised. Corrected
assertion when constructing from system and asserted calendarSystem()
is as expected.
Pick-to: 5.15
Task-number: QTBUG-88183
Change-Id: I510afcb5d9d115f68148d1f679f3224d712f92f4
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>