When set, only enforce password requirement explicitly set device-wide.
As part of the change, restructure the code such that ChooseLockGeneric
becomes the central place for aggregating password requirements from
different parties, while ChooseLockPassword only enforces whatever
password reuirement it is told (by ChooseLockGeneric via intent extras)
Bug: 169832516
Test: m RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password
Change-Id: I0acbea4819c13d4a8444c7b06928baccead18837
ff1b547548