Address visual inconsistency in smart replies

Address the major style differences and make the smart reply buttons
fit better with the other notification UI elements.

This CL does not yet address all the isues but removes the most
obvious inconsistencies.

Screenshot before: https://screenshot.googleplex.com/90QVvxJmUJ3.png
Screenshot after: https://screenshot.googleplex.com/2C8cMQgTVBG.png

Bug: 73605520
Test: In Notify post a Messaging notification with Large chices

Change-Id: Ide285c21c7bf83e9f06ade6912fd13cb3e4b9024