Modify moz-support-link

I think it would help us out if we modified moz-support-link to use in tor browser and base browser:

1. We already modify it for the help link in preferences from !807 (merged).
2. We can remove the utm parameters for mozilla links, mentioned in #41910 (closed).
3. We could use it for our own "Learn more" links, and benefit from the shared styling, etc.
4. We could better support "about:manual" links, and link to "torproject.org" website instead for base browser: mullvad-browser!118 (comment 3017289).