SystemUI: screenshot: open the screenshot instead of edit

Open the taken screenshot in gallery application when clicking on the
preview. There is a seperate edit button, so the preview imageview
should open gallery instead.

Test: atest com.android.systemui.screenshot.ScreenshotNotificationSmartActionsTest
Change-Id: I8f882ddd0da47ca50acc37d25ee0866ce5698e4f