carousel: Rework styled prev/next buttons

ivan tkachenko requested to merge work/ratijas/carousel-buttons into master

They are now filling the whole height of their parent view, they don't accept any focus to avoid UX issues, and generally have a fresh visual style.

As an experiment there is an adapter component that works in two modes: by relying on ListView's currentIndex and count, and by tracking ListView's atXBeginning/atXEnd (temporarily still needed for the old inline view).

Might now look or work the best with the old dynamically sized popup implementation, but this is gonna change in the following patches.

Breeze Light:


Breeze Dark:


Note that they are always dark in the overlay. This is very much intentional.

Breeze Light with dark buttons in the overlay:


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