Move LockSettingsService into locksettings package.

This service now has a large number of support classes so move them into
their own package to keep things tidy and easier to refactor.

Bug: 37090873
Test: runtest frameworks-services -c com.android.server.locksettings.LockSettingsServiceTests
Test: runtest frameworks-services -c com.android.server.locksettings.LockSettingsShellCommandTest
Test: runtest frameworks-services -c com.android.server.locksettings.SyntheticPasswordTests
Change-Id: Ic3cd00e6565749defd74498a3491c3d9b914ad90