Collect change before starting transition

With shell transition enabled, the previous implemented freeform and
fullscreen change transition doesn't actually work. It is necessary to
start collecting, making the server side change, before actually request
starting the transition. Otherwise, the change cannot be calculated
correctly with the necessary information.

Bug: 279803578
Test: FreeformWindowingModeTests
Change-Id: I9c25a6c30e1f5d39288d8ece4f0ca4982551d26a

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

@@ -1162,9 +1162,10 @@ class ActivityClientController extends IActivityClientController.Stub {
             }
             return;
         }
+        transition.collect(topFocusedRootTask);
+        executeMultiWindowFullscreenRequest(fullscreenRequest, topFocusedRootTask);
         r.mTransitionController.requestStartTransition(transition, topFocusedRootTask,
                 null /* remoteTransition */, null /* displayChange */);
-        executeMultiWindowFullscreenRequest(fullscreenRequest, topFocusedRootTask);
         transition.setReady(topFocusedRootTask, true);
     }