Focus context menus so screen readers can find them
Focus context menus so screen readers can find them

Fixes https://github.com/vector-im/riot-web/issues/10899

The `tabIndex` is required to make the thing actually focusable. This is the same trick employed in https://github.com/matrix-org/matrix-react-sdk/pull/2994
matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk