fix(ui): added needed markdown callbacks for web and desktop

[deven98]

Fixes #1926

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.17%. Comparing base (ce17a4e) to head (13dbef2).

Files	Patch %	Lines
...t_flutter/lib/src/message_widget/message_text.dart	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1954      +/-   ##
==========================================
- Coverage   60.18%   60.17%   -0.01%     
==========================================
  Files         317      317              
  Lines       18516    18518       +2     
==========================================
  Hits        11143    11143              
- Misses       7373     7375       +2     

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