Notification Bubble Button

Button is visible on expanded notifications that are in the
conversation section.

Always visible if the notification has metadata & the user
hasn't turned off bubbles for the device.

Button is added to end of the template actions, making it
visible if there were no other actions.

Tapping it to make a button will change the app settings
to "selected" and enable bubbles for that channel, if the
bubble wasn't allowed otherwise.

Tapping it to stop the bubble will disallow that channel
from bubbling.

Test: manual:
- check bubble button on notif with long action text
- check button is hidden when inline reply is focused
- check no bubble button on non-conversation notifs
- check create bubble from HUN
- check create bubble from expanded notif
- check that dismissing a bubble updates state of the button
- check that getting new notif after dismissing bubble
  updates state of the button

Bug: 138116133
Change-Id: Ic12204bd191530e94ea0400e16a9315a0d149252