Rework NIU Actions buttons UI

The shapes, colors, icons, and layout of the NIU Actions buttons have been updated to match the latest UI specs. The icons also no longer overlap with the layout above them, which solves a picking issue.

Bug: 186004471
Bug: 187460625
Test: Manual (tried on Wembley and Pixel 3A)
Change-Id: Ie7a0ca0c21805fc0f126053ec791fd2460710d33