Add set/verify lock credentials testAPIs in KeygyardManager

Added the following testAPIs that are guarded by
SET_AND_VERIFY_LOCKSCREEN_CREDENTIALS and
ACCESS_KEYGUARD_SECURE_STORAGE permissions:
* setLock
* checkLockCredentials

Also refactored methods out of LockPatternUtils
to LockSettingsService to allow clearing the caller identity.

Test: atest com.android.server.locksettings
Test: atest LockscreenCredentialTest
Test: atest PasswordComplexityTest after replacing usage of adb
commands with the new testAPIs
Bug: 182260585
Change-Id: Idc0432773c92ada9deb3e370526cb2ce219595dc

Change-Id: I28cbe6093a56a231022c61a6821accf01d28cda6