Fix the Mute Tab context menu item
Currently the state we display does not match the actual state of the tab. We need to update the state when opening the context menu based on the tab that the user has clicked on. Since we currently fail to do that, we are instead showing the state of whichever tab was muted or unmuted most recently rather than the state of the tab being clicked on.
This code is a little hacky as we are assigning the state of a single tab into global state, but this is not really any worse than setting global actions to be enabled/disabled based on the state of a tab, so it's no worse than the existing surrounding code.