Add class for creating unordered lists with icons instead of bullets

`.list-icon` or something like that. Let users display a list with checkmarks, stars, or other custom icons.

No file or test is named in the issue. Start by locating the existing list styling and list-related classes, then check how custom icons can be represented for unordered lists. Done means users can apply a documented class or equivalent mechanism to display checkmarks, stars, or other custom icons instead of bullets.

Written by the indexing model from the issue text.