Change the API for setting Notification Actions to be contextual.

According to Android API council we shouldn't add a new semantic-action
flag to mark an action as contextual. Instead we should use a boolean
flag.
This CL adds that boolean flag.

Bug: 120842160
Test: build and run Notify app (in
vendor/google_experimental/users/cinek/), and ensure smart actions are
showing when the 'No Smart Actions' chooser is changed to
'Short Smart Actions'.
Change-Id: I5fc6dfa37ab28e3f29529cb6fda99c049783eb80