Switch the Web Menu implementation to Base UI

[robintown]

I'm generally interested in seeing whether Compound Web components could be migrated to Base UI instead of Radix UI, as the latter is increasingly unmaintained. A good proof point for this would be our Menu components, as they have some of the most complex interaction with the Radix APIs and have outstanding issues that the move to Base UI could potentially solve for free. It will give us a good idea of the relative quality of the Base UI library.

[BillCarsonFr]

This could be benificial to the a11y epic https://github.com/element-hq/voip-internal/issues/567.
Worth investigating in that context

[robintown]

The outstanding issues with the Radix menu implementation that we see in Element Call are:

• Volume sliders in menus cannot be accessed with keyboard navigation
• Focus ring sometimes appears on the trigger after closing the menu, even when using the mouse