Add policy identifier for device policy API

Policy identifiers for DPM.getRequiredPasswordComplexity
so it can be converted into acoexistable API and utilised
by non-EMM management mode.

Bug: 289520697
Test: None
API-Coverage-Bug: 325214640
Change-Id: Idbfd8ba28765a219ca0d2e88a6b3a66fef6433a8