Always launch BlockedAppStreamingActivity as SYSTEM user

With different user the activity will be blocked which results in
infinite recursive loop.

Bug: 328298904
Test: Manually reproduced bug with Exo and tested the bugfix
Test: atest ActivityBlockingTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f44a53f962abc8af48d875c85da8a69eb3dfa23c)
Merged-In: I36761e7104418d41d22f97f82cef336833709060
Change-Id: I36761e7104418d41d22f97f82cef336833709060

services/companion/java/com/android/server/companion/virtual/VirtualDeviceImpl.java

@@ -1213,7 +1213,7 @@ final class VirtualDeviceImpl extends IVirtualDevice.Stub
         mContext.startActivityAsUser(
                 intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK),
                 ActivityOptions.makeBasic().setLaunchDisplayId(displayId).toBundle(),
-                mContext.getUser());
+                UserHandle.SYSTEM);
     }
 
     private void onSecureWindowShown(int displayId, int uid) {