[Handoff][1/N] Add FLAG_TASK_CONTINUITY

Add a new `DataSyncTypes` flag - `FLAG_TASK_CONTINUITY` - for marking associations as capable of Handoff and other task continuity sync features

Flag: android.companion.enable_task_continuity
Bug: 400970610
API-Coverage-Bug: 419601871
Test: Built - CTS tests to come
Change-Id: I642574405f069359f8f363a466fe87a74314a432