Adjust variants specs to match latest UX spec.

- hue range cutoffs are rounded (ex. 30 instead of 27)
- some changes to rotations
- vibrant theme uses the higher of the theme color's chroma or 48, 
whichever is higher.
- custom chroma for exactly one hue in the expressive neutral palette
is removed, all hues use the same chroma, removing need for 
ChromaExpressiveNeutral  
  
Bug: 213314628
Test: atest ColorSchemeTest passes. Manual testing, ex. compare
colorfulness of vibrant theme buttons in wallpaper picker before and
after change
Change-Id: I0bbec4dc9edbaa9097ad72c9b32b708db6bd064e