Enforce password complexity in lockscreen setting

Enforce a lock screen that adheres with the required complexity set by
the admin.

This is done by querying the DevicePolicyManager for the complexity set
for the given user, and merging it with the complexity from the "change
lock screen" intent (if any).

If the admin sets a higher complexity requirement than the app
triggering the lock screen change request, then the admin-set complexity
is enforced and the user is not shown information about the requesting
app.

Bug: 165573442
Test: Manually, set complexity using TestDPC and see it applies.
Test: m RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password.ChooseLockGenericTest
Test: m RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password.ChooseLockPasswordTest
Change-Id: If3f24f7430bdcbcd34265339f7d2a1ff82a44fc1