Add top level gradle files for car-setup-wizard-lib

Add top level gradle file so car-setup-wizard-lib can be built without
being imported by an external project as module.

Steps:
1.Import frameworks/opt/car/setupwizard as an gradle project in Android Studio
2.Build with `./gradlew :car-setup-wizard-lib:build` from project root
directory
3.Run tests with `./gradlew :car-setup-wizard-lib:test` from project root directory

Bug: 187445956
Test: built car-setup-wizard-lib successfully and unit tests passed
Change-Id: I6639124502adbe5edd1e9c7a7277030a4ea6a901
3 files changed