Change condition for `DomainFrontedRequests` in Lox

Currently Lox.sys.mjs uses DomainFrontedRequests if and only if TorConnect is not bootstrapped. There are a few problems with this:

1. If TorConnect is not enabled, then it will always uses DomainFrontedRequests. See related #43304.
2. DomainFrontedRequests will require user permission, as per #42606. Initially, I think this will only be needed for redeeming invites. In principle it could be extended. E.g. an option in "about:torconnect" to try and fetch newer bridges from the Lox authority if your bootstrap fails.
3. In the case of redeeming invites, similar to our discussion the other day about requesting bridges from Moat, we might want this to always use DomainFrontedRequests anyway since the user may be experiencing problems with their Tor connection.

I wonder if we should just change the condition to use DomainFrontedRequests if and only if we are redeeming and invite. Then we keep #42606 open for making sure we have user consent when lox becomes more visible in alpha or reaches the stable release.

/cc @donuts @pierov @morgan