UI Components guides

This first batch publishes 4 of the 28 upstream UI Components guides; the rest are converted and will be released in later batches.

• Accordion — “Build an accordion component with animation, optional exclusive (one-open-at-a-time) behavior, and brand-consistent styling.”
• Build a carousel — Build a carousel component that displays a set of items in a horizontal or vertical layout.
• Dialog — Build a modal or non-modal dialog component that is accessible, manages focus appropriately, and can be dismissed the way users expect on each platform.
• Tabbed interfaces — “Build a responsive tabbed interface with good UX when not all tabs fit on screen.”