Increase app icon size from 24dp to 32dp.

The app icon size as 24dp is too small. We'd like to increase to 32dp
based on latest UX feedback and to match Material Spec v2 wrt app icon
sizes.

Test: make RunSettingsRoboTest -j40 ROBOTEST_FILTER=AppPreferenceTest
Test: visual (Launch settings -> App & notification -> verify app icon
      size increased)
Fixes: 71767701

Change-Id: I474df72075602fc48d3123127b4f9bf350374506