Change the 'get_first_weekday' function to number the weekdays
Monday(1)-Sunday(7) like ISO does. Change the function name to reflect
that. Add tests for different locales, although the tests depend on
system-installed locales.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/822>
Create file to test util functions and create a test for the
gcal_date_time_from_icaltime function. The test checks if the time
zones are correctly interpreted in the conversion of an ICalTime to a
GDateTime.
mindonwarp