[ical4j 4.x] Check desugaring

[rfc2822]

Java 8 Time API requires Android 8

However it's made available on Android <8 (= Android 7, since DAVx5 requires Android 7) over desugaring.

• Check TimeZone.toZoneIdCompat method – is it still needed?
  • Otherwise replace everything.
  • Update: Can be removed with all other legacy DateTime. helpers
• Check DAVx5 sync with Android 7 when ical4j 4.x is merged.)