We patch Tor Launcher to call a helper script at the appropriate time,
and this helper will then enable/disable tor's Seccomp sandbox as
requested.

Compared to Tails' old bridge mode, we now also benefit from the
Seccomp sandbox when configuring a proxy and even when using simple
bridges. The Seccomp sandbox truly is only disabled when using
pluggable transports like obfs4 etc. that require a separate process
like obfs4proxy.

Refs: #17330