Add a feature flag for secure lock screen.

Disable certain APIs which require secure lock screen if the device
doesn't have the feature.
Make sure one cannot set the password/PIN if there is no secure lock
screen, because the password/PIN wouldn't be really used afterwards
while the password strength checks would succeed, creating a false
sense of security.
Allow setting password strength requirements in DPM - test if the
current password is sufficient will fail automatically if there is
no secure lock screen.

Bug: 111072170
Bug: 111071972
Test: cts-tradefed run cts -m CtsDevicePolicyManagerTestCases
Test: cts-tradefed run cts -m CtsAdminTestCases
Test: frameworks/base/core/tests/utiltests/runtests.sh
Test: adb shell am instrument -w -e class com.android.internal.widget.LockPatternUtilsTest com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Test: atest SyntheticPasswordTests
Test: atest LockSettingsServiceTests
Test: atest LockSettingsShellCommandTest
Test: atest DevicePolicyManagerTest (for servicestests)

Change-Id: Ie46b0de6cb03c26dd05c05711c5c3b5e36a872df