UX for tor daemon status / launch progress

[riastradh-brave]

There is no visual feedback for what the tor daemon is up to. We should:

• provide a meaningful error message if you try to use Tor before the daemon is launched,
• provide some way to query the status of the tor daemon and view log files, and maybe
• provide a display of the current circuits and exits (though perhaps that should be a separate issue).

We will want both (a) tor's stderr output, and (b) events from the control socket. I began to implement communication with the control socket in a branch a while back, but we now launch the tor daemon from C++ so that code isn't usable directly.

(This may not be worth doing at all before chromium-fork.)

[tildelowengrimm]

→ #14043