Makes legacy Injector @Injectable and adds shared singleton Preferences am: a3c0ca226b am: ac213b0b1a

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

Change-Id: I76866f5ecde4394e83432bde097a0c10f6b5fdde
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>