Fixes: #21130

Refactor carousel

drop the fixed width of the indicators. instead use the carousel-control width as margins to ensure content doesn't overlap

Move margin from adjacent selector to right on the .custom-control for better responsive rendering (#21295)

- fix naming of left/right controls
- drop the absolute positioning of things and rely on only 3d transforms
- remove img styles and require classes to avoid inline-block line-height stuff