Draft: fixup! Bug 27476: Implement about:torconnect captive portal within Tor Browser

This changelist fixes #40490 (closed) by removing our dependency on observing "network:offline-status-changed" and replaces it with a new topic "torconnect:bootstrap-complete". We add appropriate logic to BrowserGlue to trigger initialization of HTTPSEverywhere channels, and to UpdateService to trigger updates. The BrowserGlue logic happens on boot, while the UpdateService logic is triggered after update failer due to proxy server refusing connection in conjunction with bootsrap not yet having completed.

We are no longer offline by default, so we can now acquire bridges from BridgeDB before bootstrapping.

The new torconnect:bootstrap-complete topic is notified from a new TorConnect module. In the future, this module will be used to migrate much of logic currently living in the per-page aboutTorConnect.js component (so there is 1 source of truth of our current bootstrapping status to make censorship detection easier).