Polish UX of expandable switch

- Padding from the expandable arrow is now 4dp
- Arrow is pushed down 2.5dp (by modifying the drawable) to align
  with the text
- Switch and the switch divider is now fixed 36dp from top rather
  than vertically aligned

Bug: 37576453
Test: ./gradlew connectedAndroidTest test
Change-Id: Ibb3028d3bb17ca9d054911e4ff27098a200af0da