feat(accordion)!: integrate `Accordion` with v11

[metonym]

Supports #1629

This aligns Accordion with the v11 styles and API.

Breaking Changes

• Remove xl size prop. Valid sizes are sm | md | lg. Default is md.
• Remove skeleton prop. AccordionSkeleton is used separately.
• Remove $$restProps and unnecessary forwarded events.
• AccordionSkeleton is no longer open by default (flip the boolean). This more closely aligns with the AccordionItem behavior.

New Features

• Add a flush prop to flush align accordion item text.

Fixes

• Apply the layer-size class to fix sizing.
• Add an aria-controls id for the expando button.

Clean-up

• Fix JSDoc comment formatting, adjust copy where appropriate.
• Use shorthand for context instead of manually subscribing/unsubscribing.
• Improve the documentation by adding more descriptions and auditing examples.