[ical4j 4.x] Update event validators

[ArnyminerZ]

• Refactor preprocessCalendar and applyRules in ICalPreprocessor to new syntax.
• Removed the UTC validation rule since it's removed, and no longer needed after the migration to the new Java API.

[cketti]

CreatedPropertyRule was removed from ical4j 4.x. But it looks like we could use ChangeManagementPropertyValidators.CREATED instead.

[ArnyminerZ]

I wonder why we did have this rule. According to ical4j (I don't remember where I saw it) this was like this to make sure the parsing went well. With the migration to Java 8 APIs, parsing can go well even if the created dates are not UTC.

Maybe @rfc2822 has other reasons why to keep it.

[rfc2822]

We had a problem with unparsable DTSTAMP that was not a UTC timestamp once: bitfireAT/ical4android#34

And I think the CreatedPropertyRule fixed the same type of problem for CREATED.

However ical4j 4.x doesn't have problems with theses cases:

@Test
    fun testDtstampWithTimezone() {
        val iCal = "BEGIN:VCALENDAR\n" +
                "BEGIN:VEVENT\n" +
                "DTSTART:16010101T020000\n" +
                "SUMMARY:Test\n" +
                "DTSTAMP;VALUE=DATE-TIME:20220331T084614\n" +
                "CREATED;VALUE=DATE-TIME:20220331T084614\n" +
                "END:VEVENT\n" +
                "END:VCALENDAR\n"
        val cal = CalendarBuilder().build(StringReader(iCal))
        val e = cal.getComponent<VEvent>(Component.VEVENT).get()
        assertEquals("20220331T084614Z", e.dateTimeStamp.value)
        assertEquals("20220331T084614Z", e.created.value)
    }

So I think it's fine to remove that rule.