Advanced Search Panel - 2.1.1 Keyboard - Chevrons do not collapse on user input once expanded

[imogenroberts]

As a user reliant on the keyboard to access content, the keyboard should offer users the same facilities as users who are able to use a mouse.

Linked work item:
#9386

Expected Result:
Using the mouse allows the user to expand and collapse chevrons - the keyboard should offer users the same facility.

Actual Result:
If the user types a search term into the advanced search bar, all search results are displayed below the appropriate chevrons. However, despite the user being able to focus on the search result headings ('SeparateCards', etc.), the chevrons do not expand or collapse the headings if the user hits Enter on the keyboard.

Evidence:

[imogenroberts]

RETEST: Chevrons are now collapsible/expandable using the keyboard.

Evidence: