Fix back gesture/dismiss button in screenshot shelf UI

Bug: 334877806
Bug: 329659738
Test: manual (testing back gesture/touch interaction)
Flag: ACONFIG com.android.systemui.screenshot_shelf_ui DEVELOPMENT

Change-Id: I01ff75588b01bb34428d3cffa3ce5f0712bb7f72
Merged-In: I01ff75588b01bb34428d3cffa3ce5f0712bb7f72
5 files changed