Improve DropdownMenu accessibility state

[web3blind]

Summary

• expose aria-expanded, aria-haspopup, and aria-controls on the DropdownMenu trigger when possible
• give the rendered menu a stable id so the trigger can reference the open menu
• mark the visual check icon as decorative and expose selected items with aria-current

Accessibility impact

This improves screen reader feedback for DropdownMenu users by announcing whether the trigger opens a menu and whether it is currently expanded. It also avoids the Material Icons check glyph being announced as extra text for selected entries.

Partially addresses #183. The remaining larger work around focus trapping, Tab behavior, and menu item semantics can be handled separately.

Checks

• corepack yarn -s tsc --noEmit
• corepack yarn -s lint (passes with existing warnings in preview components)
• corepack yarn -s test

[web3blind]

Closing this older iteration in favor of #229, the latest consolidated dropdown accessibility PR.