SearchManagerService made multi-user aware

Cache Searchables per user and query package manager through the
private interface.

Change-Id: I1d24fdd27cce8c27be45287cbfcb4df1e2ce2cf1

services/java/com/android/server/pm/PackageManagerService.java

@@ -9383,7 +9383,7 @@ public class PackageManagerService extends IPackageManager.Stub {
 
     @Override
     public UserInfo getUser(int userId) {
-        enforceSystemOrRoot("Only the system can remove users");
+        enforceSystemOrRoot("Only the system can query user");
         return sUserManager.getUser(userId);
     }