Tweak accessibility in for call blocking settings.

+ Adjust talkback focus to allow the user to page through the cards
for the settings and import separately, even though they are
structurally part of the same header component, visually they
reside in different "cards".

+ Change the "hide setting" to be toggled by tapping on the text
description area.

Bug: 25163592
Change-Id: I0d1fcd28dba058d707bfe5099cdf912aed14f728