Changed AuthPasswordSyntax*.decodeAuthPassword() return type from StringBuilder[] to String[]

AuthPasswordSyntaxImpl.java, AuthPasswordSyntax.java:
Changed decodeAuthPassword() return type from StringBuilder[] to String[].
It is now inline with UserPasswordSyntax.decodeUserPassword(), which is what client code expects anyway. This dramatically simplifies client code.

*.java:
Deduplicated AuthPassword vs. UserPassword code paths by extracting methods that check the pwPolicyState.getAuthenticationPolicy().isAuthPasswordSyntax()) method and choose one code path or the other.