Auto hide IllustrationPreference when lottie file is empty

Flag: com.android.settingslib.widget.flags.auto_hide_lottie_res
Bug: 337873972
Test: unit test
Test: manual: delete `lottie_adaptive_brightness.json` from overlay, navigate to Display > Adaptive Brightness -- verify no empty container
Change-Id: I873976d3e87b119a3ee690d95c68149f249fe7a9
5 files changed