Add new preview for custom theme page (part1)

- Add new preview to the naming page, and wait decision for other pages.
- Screenshot: https://screenshot.googleplex.com/RwTqj6Q1Eiz.png
- Next: make shape app icon names available for the custom theme preview info.

Test: Manually
Bug: 151285476
Change-Id: Icc43bfbacd00d9180ae51da702b9bf8c6dd9d27e