[CD] Fix predictive back system anims partially run on wrong display

Bug: 382774299
Test: Manual, i.e. verified that predictive back system animations do
      not add background/scrim windows on the wrong display.
Flag: com.android.window.flags.enable_multidisplay_trackpad_back_gesture
Change-Id: I833a7d93c5fe30287cb8ec2bf0b4eea803a659a1