Add urlbar quick actions for Tor Browser

Mozilla has some quick actions that can be triggered via the urlbar. E.g. if you type "help" a "Tor Browser help" action will appear.

We should consider whether to add our own actions for Tor Browser. Some ideas:

1. An action for Tor bridges. Just a shortcut to the "Bridges" settings.
2. An action for opening the Tor Browser manual about:manual. Would show alongside "Tor Browser help" if the user types "help".
3. A "Change language" option to change the browser's language. Not sure about whether switching languages is a pain point or not.

/cc @donuts @felicia @morgan