Write a valid VTIMEZONE on Windows CE

    On Systems that do not provide a valid database about
    Timezone transitions the VTIMEZONE entry of the ical
    data would only contain the Tzid.

    For WinCE there is now a fallback to write the current Timezone
    information in the entry. This works since the gui on WinCE
    does not offer the user to create an Event in a different Timezone.

    I've added the code here in kcalcore instead of KTimeZone because
    this is tailored specifically to what the ical format requires
    and can not be generalized to other timezones then the current
    Zone.

    BUG: 263018