www/tor-browser: various improvements

• use a dedicated directory [1]
• enable building without PulseAudio, use Gecko framework more [2]

No PORTREVISION bump because the next commit will update the port
to a new version.
PR: 268584 [1]
PR: 268245 [2] (attachment 3)
Approved by: maintainer timeout (freebsd@sysctl.cz, 6 weeks)