Add hidden KeyProtection API to specify SID

Allows the caller to specify which SID the given key
should be bound to, overriding the default rule of
binding to the current root/fingerprint SID.

This is a prerequsite for introducing synthetic password
based authentication flow.

Test: cts-tradefed run cts -m CtsKeystoreTestCases
Bug: 33126414
Change-Id: Ide03c0f4fd33ecca7a169ea763c3d4d0b173d1dd

keystore/java/android/security/GateKeeper.java

@@ -29,6 +29,8 @@ import android.service.gatekeeper.IGateKeeperService;
  */
 public abstract class GateKeeper {
 
+    public static final long INVALID_SECURE_USER_ID = 0;
+
     private GateKeeper() {}
 
     public static IGateKeeperService getService() {