fix daylight time in QTimeZone on Android

Android does not provide an API to access daylight time transitions,
so the standard QTimeZonePrivate::dataForLocalTime only returns
standard time without the daylight offset

Therefore provide an override,
QAndroidTimeZonePrivate::dataForLocalTime, which tests daylight time
offsets directly rather than using transitions.

Change-Id: Ia8adaf9af40da38aadfa7d22d9a3fe9da9ba24a8
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>