API to query "Reduced Motion" preferences

Virtually all desktop and mobile platforms have a way for the user to configure that they prefer the UI to avoid motion-based animations. This is primarily for accessibility reasons.

See https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion for more details on this.

As far as I can tell Qt offers no API for developers to query this preference from the platform and adjust accordingly.

Qt should have API to expose this information to application developers and use it internally wherever it uses motion-based animations.

See also https://github.com/flatpak/xdg-desktop-portal/pull/1590 which prompted this