DO NOT MERGE Make dialpad slide down when dismissed by tapping outside

The dialpad currently simply disappears from view immediately when
dismissed by tapping in the space above it. instead, it should
slide downwards.

Cherry-pick from https://googleplex-android-review.git.corp.google.com/#/c/430822/

Bug: 13419260

Change-Id: Ibc248f7c36289e151e0ea41b2bb32e64dcb07088