Backport of sabre-io/vobject#716 -- support RDATE together with RRULE.

[rotdrop]

Please refer also or even primarily to the discussions of the respective issues and PRs of the upstream Sabre project:

• issue Composing multiple RDATE and RRULE properties sabre-io/vobject#347
• issue RRULE with RDATE / EventIterator.php sabre-io/vobject#700
• PR Support concurrency of multiple RDATE together with RRULE directives. sabre-io/vobject#716

This is a backport of the (not yet accepted) PR sabre-io/vobject#716

The base of the PR is that in my user community we have a wild mixture of users (Windoze, half-eaten-apple, me as Linux guy), and this case of mixed RRULE and RDATE just occurs, example:

DTSTART;TZID=Europe/Berlin:20250703T190000
DTEND;TZID=Europe/Berlin:20250703T210000
RRULE:FREQ=WEEKLY;UNTIL=20370101T225959Z;INTERVAL=4;BYDAY=TH
RDATE=;TZID=Europe/Berlin:20250424T193000

This is fully supported by the CalDAV standard which states that the total recurrence-set is just the union of the events defined by RRULE as well as RDATE directives.

[rotdrop]

Oops. This should be modelled in the context of cweagans/composer-patches. Ok. I'll eventually do this.

[rotdrop]

Oops. This should be modelled in the context of cweagans/composer-patches. Ok. I'll eventually do this.

Refactored using composer-patches framework.

[SebastianKrupinski]

Hi @rotdrop

We are not apposed to these changes but will need to review and test them first.

Please give us a bit of time to do so.

[SebastianKrupinski]

@rotdrop

I commented on your PR in the SabreDAV repo.