fix(ui): added scrolling to reactions

[deven98]

Added scrolling if reaction count is high.

[codecov]

Codecov Report

Attention: Patch coverage is 72.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 60.28%. Comparing base (099667f) to head (9f7701a).
Report is 14 commits behind head on master.

Files with missing lines	Patch %	Lines
.../src/message_widget/reactions/reaction_picker.dart	72.00%	7 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2045   +/-   ##
=======================================
  Coverage   60.28%   60.28%           
=======================================
  Files         318      318           
  Lines       18583    18584    +1     
=======================================
+ Hits        11202    11203    +1     
  Misses       7381     7381           

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