Make displayChange in existing transition just an error.

This doesn't need to crash the system. It should be an error,
though. Unfortunately, display-changes, currently are not
deferrable so we can't guarantee a unique transition.

Bug: 259004137
Test: systemui-foldable-smoke-suite
Change-Id: Iea946724fa949d731f05f1f975ffd8b338f78684

services/core/java/com/android/server/wm/TransitionController.java

@@ -423,7 +423,7 @@ class TransitionController {
         Transition newTransition = null;
         if (isCollecting()) {
             if (displayChange != null) {
-                throw new IllegalArgumentException("Provided displayChange for a non-new request");
+                Slog.e(TAG, "Provided displayChange for a non-new request", new Throwable());
             }
             // Make the collecting transition wait until this request is ready.
             mCollectingTransition.setReady(readyGroupRef, false);