Move webrtc options from advanced to security prefs

[diracdeltas]

fix #13805

Test Plan:

1. go to about:preferences > Advanced
2. you shouldn't see webrtc options there
3. go to about:preferences > security
4. you should see the webrtc options

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed. (Ask a Brave employee to help if you cannot access this document.)

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[codecov-io]

Codecov Report

Merging #13807 into master will decrease coverage by <.01%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           master   #13807      +/-   ##
==========================================
- Coverage   56.55%   56.54%   -0.01%     
==========================================
  Files         283      283              
  Lines       28799    28798       -1     
  Branches     4774     4774              
==========================================
- Hits        16286    16284       -2     
- Misses      12513    12514       +1

Flag	Coverage Δ
#unittest	56.54% <25%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
app/renderer/components/preferences/advancedTab.js	47.54% <ø> (-0.9%)	⬇️
js/about/preferences.js	61.25% <25%> (-0.36%)	⬇️

[bsclifton]

Works great! ++

[bsclifton]

master 0b28df1
0.23.x 3133520
0.22.x cd75af0