Screenshot Notification Smart Action: AiAi and - Sys UI integration

This change creates ScreenshotNotificationSmartActionsProvider, which is overridden
in GoogleSystemUI.
Calling AiAi is guarded by a device config flag created in cl/277143225.

Test: Manually tested the code in this CL and corresponding change in SystemUIGoogle.
Took a screenshot and verified that AiAi gets invoked and the screenshot notification
shows smart actions.
Ran new tests added in this CL 'atest ScreenshotNotificationSmartActionsTest'
Bug: 143556894

Change-Id: I439a4be9aac53fb02b566ae4d438afe3edf2b37a