web: refresh key grabs after updating focus

When the web script is reactivated, refreshKeyGrabs is called, but locusOfFocus might not yet be set to the currently active control, so the script doesn't know that structural navigation is active, meaning that at-spi isn't instructed to add the key bindings for structural navigation. Later, onFocusedChanged is called, and it might update locusOfFocus without notifying. We need to ensure that the AT-SPI key grabs are updated in this case.