Keyboard Accessibility in Modals - SHIFT + TAB should cycle backwards

Created by: DavidMacDonald

• Operating system and version : All versions

• Browser and version : All versions

• Test case: Launch demo modal and Press Shift+Tab https://getbootstrap.com/docs/4.0/components/modal/

• Expected Result: When focus leaves first interactive element, it should go to the last interactive element.

• Actual Result: Focus stops on the first interactive element and no further action can be taken with SHIFT +TAB