feat: firefox conference calling

[z-dule]

Call into AVS for checking if conference calling is available.
This will allow us to even enable conference calling in Firefox, as AVS will do the browser specific checks.

Use only together with AVS 9.5.x and higher.

[codecov]

Codecov Report

Merging #16015 (09735a2) into dev (189d35f) will increase coverage by 0.01%.
Report is 2 commits behind head on dev.
The diff coverage is 100.00%.

❗ Current head 09735a2 differs from pull request most recent head cef40fa. Consider uploading reports for the commit cef40fa to get more accurate results

@@            Coverage Diff             @@
##              dev   #16015      +/-   ##
==========================================
+ Coverage   44.77%   44.79%   +0.01%     
==========================================
  Files         700      701       +1     
  Lines       23308    23302       -6     
  Branches     5297     5289       -8     
==========================================
+ Hits        10437    10438       +1     
+ Misses      11510    11504       -6     
+ Partials     1361     1360       -1