styles: Clean up thumbnail variables
- Use skin variable design tokens where available and add them into the Less files instead of the variables file. They should be the standard call.
- Rename variables file to clearer communicate its scope. In future we'd like to aim for replacing the file completely.
- Remove indirection of variables inside variables for readability.
- Add and change a few print specific variables. Design Systems Team also aims for standardizing those in future, see T350748.
Co-Authored-by: Volker E. <volker.e@wikimedia.org>
Change-Id: I96e073234eb62ad968adb7f87e9c9d1082febb3c