Initial definition of DevicePolicySafetyChecker.

This object will be used to fail DevicePolicyManagers that cannot be
executed on automotive when it's not safe to (for example, because
the vehicle is moving).

Test: atest CarDevicePolicyManagerTest#testLockNow_safe \
            CarDevicePolicyManagerTest#testLockNow_unsafe
Bug: 172376923

Change-Id: I7f910a7ee5efc7d647525db1687bd27e68cb7c0a