alternatecalendar: add support for Islamic Calendar (Astronomical and Umm al-Qura)

There are different kinds of Islamic calendars, and Qt only supports
"Islamic calendar, tabular". This adds support for another two Islamic
calendars.

The Islamic religious calendar and Saudi Arabia's Umm al-Qura
calendar, however, are based on the observation of the crescent moon.
It is thus affected by the position at which the observations are
made, seasonal variations in the time of sunset, the eccentricities of
the moon's orbit, and even the weather at the observation site. This
makes it impossible to calculate in advance, and it causes the start
of a month in the religious calendar to differ from the civil calendar
by up to three days.

Using astronomical calculations for the position of the sun and moon,
the moon's illumination, and other factors, it is possible to
determine the start of a lunar month with a fairly high degree of
certainty. However, these calculations are extremely complicated and
thus slow, so most algorithms, including the one used here, are only
approximations of the true astronomical calculations. At present, the
approximations used in this class are fairly simplistic; they will be
improved in later versions of the code.

Like the Islamic religious calendar, Umm al-Qura is also based on the
sighting method of the crescent moon but is standardized by Saudi
Arabia.

See also: https://cldr.unicode.org/development/development-process/design-proposals/islamic-calendar-types
and https://developer.android.com/reference/android/icu/util/IslamicCalendar

FEATURE: 72418
FIXED-IN: 6