add toggle to combobox trigger

[sethhorsley]

This pull request updates the combobox component to improve accessibility and user interaction by ensuring the popover's open/close state is consistently tracked and toggled. The main changes involve synchronizing the aria-expanded attribute with the popover state and refactoring the trigger action to toggle the popover instead of just opening it.

Accessibility and popover state management:

• Added a new handlePopoverToggle method in combobox_controller.js to keep the aria-expanded attribute of the trigger element in sync with the popover's actual state.
• Modified the popover's default attributes in combobox_popover.rb to trigger handlePopoverToggle when the popover is toggled.

Refactoring trigger and popover logic:

• Changed the trigger's action in combobox_trigger.rb from openPopover to togglePopover, allowing users to both open and close the popover via the trigger.
• Refactored the popover logic in combobox_controller.js by introducing a new togglePopover method, which checks the current state and calls either openPopover or closePopover as appropriate.

[cirdes]

really nice!!