Removed the notification action background

Also added conditional paddings when inline
replying, such that the layout looks good.
This refactors the overall layout design and ensures
that smart replies and other content that is on
the bottom are always visible.

Bug: 69168591
Test: add notification, reply, no action background
Change-Id: I83d3f0d2512f0cf8c8b9db0edc7b27cbb109aeb9