Include IWindowContainer token along with StackInfo

This is needed for stacks to participate in transactions.
Most immediate use-case will be PiP during rotation

Bug: 119687367
Test: Added ActivityTaskManagerServiceTests#testStackTransaction

Change-Id: I50a5c3cea4f23f2be4e55ba38f8a5371fa9dfe79
diff --git a/services/core/java/com/android/server/wm/RootActivityContainer.java b/services/core/java/com/android/server/wm/RootActivityContainer.java
index 5a21016..06cce52 100644
--- a/services/core/java/com/android/server/wm/RootActivityContainer.java
+++ b/services/core/java/com/android/server/wm/RootActivityContainer.java
@@ -1250,6 +1250,7 @@
         stack.getBounds(info.bounds);
         info.displayId = displayId;
         info.stackId = stack.mStackId;
+        info.stackToken = stack.mRemoteToken;
         info.userId = stack.mCurrentUser;
         info.visible = stack.shouldBeVisible(null);
         // A stack might be not attached to a display.