Move SliceStore notification and activity to a separate app

Android does not allow privileged processes to display a WebView in an
activity. Move the notification logic and SliceStoreActivity to a
separate app and send responses back to SliceStore instead.

Test: atest TelephonyManagerReadNonDangerousPermissionTest
Test: Manually verify notification click, manage, timeout, cancel
Test: Manually verify premium capability throttle, pending, unsupported
Test: Manually verify WebView shows up when activity starts
Test: Manually verify notification/activity behavior with multi user
Bug: 245882092
Bug: 245882601
Change-Id: Ia20a48a446e9075d0931e2efa299c4b0223e5a12