Synchronize without `Event` data class (#1783)

* [WIP] Proof of concept for syncing without `Event` data class

* Replace AndroidEvent2 with EventsContract

* Update synctools, refactor upload logic in `CalendarSyncManager`

* KDoc

* Update UID immediately in `ContactsSyncManager`, `CalendarSyncManager`, and `TasksSyncManager`

- Remove `OnSuccessContext.uid` from `GeneratedResource`

* Minor changes

* Handle multiple events in a single iCalendar

- Rename `processVEvent` to `processICalendar`
- Add default alarm for non-full-day events again
- Prevent NPE on null flags (used for debug info)

* Fix tests