Draft: Run Tor Browser in pseudo flatpak

Closes #19266, #15678, #19255 (closed), #19408, #19572

Partly solves:

• #10422 except for these subtasks:
  • Remove the "Tor Browser" and "Tor Browser (persistent)" folders (see #15028)
  • Update doc
• #19328 except for the Unsafe Browser part

TODO:

• Rename strings in deploy data
• See if we can get Tor Browser to use Unix sockets instead of ports for the SOCKS port and control port (#19405)
  • Would allow us to get rid of the special network namespace handling
  • Not required for this MR