Ensure bubble bar gets excluded from the screenshot in app clips

Flag: com.android.wm.shell.bubble_bar
Test: manual - enable bubble bar
             - get a bubble that supports app clips
             - tap the app clip button
             => verify that bubble UI isn't in the screenshot
Bug: 343753351
Change-Id: Ifc2a424a572a174a5fe6a34485f33f34bf279f1d