[combobox] Fix accessibility issues

[jpzwarte]

• aria-current is not supposed to be used in combination with the option role (https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-current#associated_roles)
• VoiceOver says "Dialog not selected, selected, current item (8 of 35)"; figure out why it says "not selected, selected"
• Check if keyboard navigation can be improved; feedback: "So when you navigate into the input, you can press backspace and you land on the last tag. Seen with the focus here. When it’s focused, you can press backspace and delete. Or you can use arrow keys to navigate to one of the other items."
• The popover is too small in Safari; only the first option is visible
• "You are currently on a selectable (null), inside a list box."

[furstenberg]

I have another possible issue when using the virtual list.

Steps:

• add items
• Shift-TAB to land on item
• Press ENTER when X has focus
• Notice how remaining item is now no longer in the tab order.

https://github.com/user-attachments/assets/fb827144-8c9a-48cf-986b-64570e89bf81

[furstenberg]

Related (?) issue seen in combobox-multiple-basis:

In Safari (v18.1.1) on macOS 15.1.1:

• Add two items
• Remove first item

Observe both items be removed.

https://github.com/user-attachments/assets/7403e912-82c2-4c7b-a0d8-20c92fd78f53