Expose TZ info on control port for better debugging of time errors

When we tell people that their clocks are wrong, it's frequently because they've set up their systems with the wrong time zone. It would be helpful to tell torbrowser (or some other controller) about this information, so that it can give more useful error messages on time-related bootstrapping failures.

One complication here is (IIUC) TB runs, and runs tor, with its TZ set to UTC.

Further investigation suggests that TB might not set TZ for the first time it starts tor. Opened #25823 (moved) for the Tor Launcher behavior inconsistency.