Popup keyboard navigation bug

[Malvoz]

https://maps4html.org/experiments/screenreader/restaurants/

Repro steps:

1. Tab to the The Prescott marker and press enter or space to open the popup
2. Tab twice to focus the Focus Map control
3. Tab backwards once to focus the The Prescott link inside the table
4. Popup closes

Expectation

On step 4. the popup should remain open and the The Prescott link should have focus.

[Malvoz]

I'm inclined to close this out as wontfix, because #535 suggests the removal of the popup navigation controls which I believe is the source of this bug.