Apply transaction before calling onFinish

A split pair may be dismiss in the background and the stage will skip
the fade out transition. This will cause onFinish being executed
immediately. So move the apply transaction operation before requesting
fade out to ensure the order of execution.

Bug: 269126417
Test: nexus_oop_test_multi_device_platform
Change-Id: I696a38fb6ab4d702127b530cd4a20492b5ad09aa
Merged-In: I696a38fb6ab4d702127b530cd4a20492b5ad09aa
(cherry picked from commit 4ff27cb758)

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/SplitScreenTransitions.java

@@ -193,6 +193,8 @@ class SplitScreenTransitions {
             mAnimatingTransition = transition;
             mFinishTransaction = finishTransaction;
 
+            startTransaction.apply();
+
             final SplitDecorManager topDecor = mPendingDismiss.mDismissTop == STAGE_TYPE_MAIN
                     ? mainDecor : sideDecor;
             topDecor.fadeOutDecor(() -> {
@@ -200,8 +202,6 @@ class SplitScreenTransitions {
                     onFinish(null /* wct */, null /* wctCB */);
                 });
             });
-
-            startTransaction.apply();
         } else {
             playAnimation(transition, info, startTransaction, finishTransaction,
                     finishCallback, mainRoot, sideRoot, topRoot);