Change position of "answer as video" to swipe right.

In b/21124069, a change was made to make swipe-right default to answer
as audio, and swipe down be answer as video for a video call.

UX expressed that it makes more sense to use the previous swipe-right to
answer as video and swipe down to answer as audio.

Bug: 27097678
Change-Id: Id495d985dfb5c6dafdf45493ce37ad8b47dd5f7e