ical-recurrence: test that Count takes the chronologically first yearly instances
The BYWEEKNO branch of yearlyDayCandidate iterates over the days of the
week in Monday-to-Sunday order regardless of the week start, so with
WKST=SU it emits Sunday last while Sunday is chronologically first.
recurUntil and recurCount both assume the list of occurrences ascends.
recurCount then takes the wrong instances, and recurUntil is worse: it
returns the empty set at the first element past UNTIL, so one
out-of-order day truncates everything after it. The same ordering also
mis-numbers BYSETPOS in that branch.
monthlyDateTimeRecurrence and weeklyDateTimeRecurrence sort their
candidates before use; yearlyDateTimeRecurrence does not.
With a week start of Sunday, week 1 of 2021 starts on Sunday the 3rd of
January and week 1 of 2022 on Sunday the 2nd, so counting from the
Sunday of week 1 of 2021 the next two instances are the Monday after it
and the Sunday of week 1 of 2022.