[FIX] Emoji rendering on reactions

[sampaiodiego]

Proposed changes (including videos or screenshots)

The issue is when using a CDN, the CDN_PREFIX setting value can be a full domain (i.e.: https://my-cdn.rocket.chat), which will make the split(':') do unintentional splits, causing the issue.

I changed to just use emojiElement.style.backgroundImage in case it is available but kept the old way to get the backgroundImage just in case.

Issue(s)

Steps to test or reproduce

Further comments

[codecov]

Codecov Report

Merging #27863 (e96cb9d) into develop (7ecedc4) will increase coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop   #27863      +/-   ##
===========================================
+ Coverage    43.18%   43.20%   +0.02%     
===========================================
  Files          818      818              
  Lines        17147    17148       +1     
  Branches      1945     1946       +1     
===========================================
+ Hits          7405     7409       +4     
+ Misses        9475     9473       -2     
+ Partials       267      266       -1     

Flag	Coverage Δ
e2e	43.20% <0.00%> (+0.02%)	⬆️

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