Classify PINNED as a transient windowing mode.

Since we now perform setWindowingMode for PIP (even for the case of
re-parenting, we move the activities to a new stack first and then set
its windowing mode to PINNED), we can now add this condition.

Bug: 114842032
Bug: 144508210
Test: Try to do repro steps on b/144508210, no longer happens.
Change-Id: I0e491c52273e9d5edef05b1745c5fbffd9361ac0

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

@@ -808,8 +808,8 @@ class ActivityStack extends WindowContainer<WindowContainer> implements BoundsAn
      * @return {@code true} if the windowing mode is transient, {@code false} otherwise.
      */
     private static boolean isTransientWindowingMode(int windowingMode) {
-        // TODO(b/114842032): add PIP if/when it uses mode transitions instead of task reparenting
-        return windowingMode == WINDOWING_MODE_SPLIT_SCREEN_PRIMARY
+        return windowingMode == WINDOWING_MODE_PINNED
+                || windowingMode == WINDOWING_MODE_SPLIT_SCREEN_PRIMARY
                 || windowingMode == WINDOWING_MODE_SPLIT_SCREEN_SECONDARY;
     }