Add CUJ_BACK_PANEL_ARROW for tracking jank

Also:

 - Fix possible NPE in InteractionMonitorDebugOverlay

 - Add logging to InteractionMonitorDebugOverlay because the back arrow
   window is small, so reading logcat is easier.

Test: atest SystemUITests
Bug: 304583132
Bug: 304582856
Flag: ACONFIG com.android.systemui.edge_back_gesture_handler_thread DISABLED
Change-Id: Id13f7274a8c50d936fa97d8a54bc4f310728dfda