Announce collapsible sections in the docs menu

[damianstasik]

Checklist

• I have read the contribution guide.
• I have not used an AI coding assistant to create this PR.
• My contribution is compatible with the MPL-2.0 license and I have provided a DCO sign-off on all my commits.
• I have written all code in this PR myself OR I have marked all code I have not written myself (including modified code, e.g. copied from other places and then modified) with a comment indicating where it came from.

[cloudflare-workers-and-pages]

Deploying registry-ui with    Cloudflare Pages

Latest commit:	b5cd236
Status:	✅  Deploy successful!
Preview URL:	https://b7853089.registry-ui-dxi.pages.dev
Branch Preview URL:	https://improve-docs-menu-a11y.registry-ui-dxi.pages.dev

View logs

[abstractionfactory]

Did a quick test with NVDA, this is better. It announces as "Button collapsed resources" and if you press it, it says "Expanded". The sublist is announced as "List with x items"