Prevent NullPointerException from long tap on destroyed window decoration.

The long tap event could be delivered after the window decoration was
destroyed and removed from DesktopModeWindowDecorViewModel. This change
ensures the long tap is canceled during destruction, preventing the
listener from accessing a non-existent DesktopModeWindowDecoration.

Bug: 397767291
Test: None
Flag: com.android.window.flags.enable_desktop_windowing_mode
Change-Id: I55286357680e8ae9cfddb5e84d4a637931b28fa1