Ensure move-to-back has its own transition.

In general, we need to move to a model where each transition is
a "fixed" transaction (rather than absorbing everything within
a specific time-window).

Bug: 232020248
Test: PinnedStackTests#testMovePipToBack*
Change-Id: Icf5d36e507bc70736e7760c50d5de297bfe4d8f4

data/etc/services.core.protolog.json

@@ -163,6 +163,12 @@
       "group": "WM_ERROR",
       "at": "com\/android\/server\/wm\/WindowManagerService.java"
     },
+    "-1941440781": {
+      "message": "Creating Pending Move-to-back: %s",
+      "level": "VERBOSE",
+      "group": "WM_DEBUG_WINDOW_TRANSITIONS",
+      "at": "com\/android\/server\/wm\/Task.java"
+    },
     "-1939861963": {
       "message": "Create root task displayId=%d winMode=%d",
       "level": "VERBOSE",
@@ -2917,12 +2923,6 @@
       "group": "WM_DEBUG_LOCKTASK",
       "at": "com\/android\/server\/wm\/ActivityTaskManagerService.java"
     },
-    "716528224": {
-      "message": "Focused window found using wmService.getFocusedWindowLocked()",
-      "level": "DEBUG",
-      "group": "WM_DEBUG_BACK_PREVIEW",
-      "at": "com\/android\/server\/wm\/BackNavigationController.java"
-    },
     "726205185": {
       "message": "Moving to DESTROYED: %s (destroy skipped)",
       "level": "VERBOSE",