Makes legacy Injector @Injectable and adds shared singleton Preferences am: a3c0ca22

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/24480169



Change-Id: I210b267582c22b7e0446b6b343fcacf1d26d5353
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>