[Collapsible] Add Collapsible components and hooks

[mj12albert]

Closes https://github.com/mui/base-ui/issues/84

Docs: https://deploy-preview-481--base-ui.netlify.app/base-ui/react-collapsible/

Extra demos:

• Animated with framer-motion: https://deploy-preview-481--base-ui.netlify.app/experiments/collapsible-framer/
• Crude accordion using 3 Collapsibles + CSS transitions: https://deploy-preview-481--base-ui.netlify.app/experiments/collapsible-accordion/
• hidden="until-found": https://deploy-preview-481--base-ui.netlify.app/experiments/collapsible-hidden-until-found/

• [x] I have followed (at least) the PR section of the contributing guide.