Use case

The current DropdownMenu implementation wrapped the trailing icon in an IconButton. Because both the TextField and the IconButton are focusable by default, this led to several focus issues.
it would be better if the icon was not a button by default.

Quoting @davidhicks980 from #172753 (comment).

"most comboboxes in the wild default to an unfocusable "button" that usually only opens the listbox when clicked"

Some examples:

• https://www.w3.org/WAI/ARIA/apg/patterns/combobox/examples/combobox-autocomplete-list/
• https://react-spectrum.adobe.com/react-aria/ComboBox.html#menu-trigger-behavior

On MacOS:
https://github.com/user-attachments/assets/7738df66-c144-42aa-b8ee-d4d229915d43

From WAI:
"The button has been removed from the tab sequence of the page, but is still important to assistive technologies for mobile devices that use touch events to open the list of options."

Proposal

Make the DropdownMenu trailing icon not focusable by default.