Move SmartReplyView inflation off the UI thread.

To avoid blocking the UI thread we here move the inflation of
SmartReplyView and its smart suggestion buttons off the UI thread.

We move these inflations into NotificationContentInflater where they are
performed before the inflations of other notification content views -
reusing the existing AsyncTask to run these inflations on a background
thread.
More specifically: for both the expanded state and the heads-up state of
a notification we
    1. inflate a SmartReplyView,
    2. inflate the buttons within that view (reply buttons and action
    buttons), and
    3. create a SmartRepliesAndActions object
from the AsyncTask (on a background thread). We then pass these objects
back to the UI thread where we attach them to the view hierarchy or use
them to make certain decisions.

In terms of thread-safety the background thread reads constants from
SmartReplyConstants so that class must be thread-safe (at least so that
the background thread doesn't store a local copy of the constants).
We also pass a SmartReplyController reference on the background thread,
that reference is only used on the UI thread (in onClick listeners).

Bug:119801785
Test: post message notification containing smart replies and actions.
Post both heads-up and notification shade notifications. Click on
replies and actions. Ensure the smart-buttons are updated when a
notification is updated.

Change-Id: I4698a6895cf65c46461cc429b2b6eb5905acb629