Suggest smart actions in ExtServices

By using text textclassifier API, we classify entities like
email, phone, address in the notification and suggest the corresponding
actions.

Test: Manual test for now. Sideload GoogleExtServices. Write a sample app
to generate notification with phone number / address, etc, and finally
observe the smart actions.

BUG: 110527159

Change-Id: I02740cb07fa25a588d9e864990f95332d6830f12