Use current user isntead of system user if no --user parameter is passed

This is relevant when running cts tests in instant mode.
Certain tests were failing in non-system users in instant mode, which is particularlly consquential to auto.
THis fix will be cherry-picked back to their repo
Test: CTSAccessibility*, in both instant/non-instant, and with both system and secondary users.
Bug:146218533

Change-Id: I89937bd552d372adc5d96c51b24d1a2bb4a034e3

services/accessibility/java/com/android/server/accessibility/AccessibilityShellCommand.java

@@ -17,6 +17,7 @@
 package com.android.server.accessibility;
 
 import android.annotation.NonNull;
+import android.app.ActivityManager;
 import android.os.ShellCommand;
 import android.os.UserHandle;
 
@@ -83,7 +84,7 @@ final class AccessibilityShellCommand extends ShellCommand {
                 return null;
             }
         }
-        return UserHandle.USER_SYSTEM;
+        return ActivityManager.getCurrentUser();
     }
 
     @Override