GlPopover: Focusable elements within a popover are not focusable
Currently, the popover itself appears far down in the markup, making it not accessible after tabbing past the button triggering it. We should make focusable elements within a popover accessible by keyboard after tabbing the button that triggers the popover. Came out of gitlab!51003 (comment 515626842).
Although, I don't know if this is possible, since the popover doesn't contain both the button and popover, it will be different on a case by case basis, making it difficult to account for the structure and situation.