Add toggle icon

[ahuang11]

Closes #6022

To be used for ChatReactionIcons

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (3448cdd) 84.67% compared to head (98ebe5a) 84.70%.

Files	Patch %	Lines
panel/tests/ui/widgets/test_icon.py	94.23%	3 Missing ⚠️
panel/chat/icon.py	94.11%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6034      +/-   ##
==========================================
+ Coverage   84.67%   84.70%   +0.03%     
==========================================
  Files         291      295       +4     
  Lines       43816    43885      +69     
==========================================
+ Hits        37101    37173      +72     
+ Misses       6715     6712       -3     

Flag	Coverage Δ
ui-tests	40.72% <58.43%> (+0.07%)	⬆️
unitexamples-tests	72.80% <68.67%> (-0.06%)	⬇️

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[philippjfr]

Good start! Next we probably have to create and sync a bunch properties between this wrapper and the underlying icon model.

[ahuang11]

Okay this is ready for the next release I think! Feel free to make changes directly as needed.

A couple notes for future enhancements: #6037

1. if the icon does not exist, it shows absolutely nothing
2. support SVG

ToggleIcon

Screen.Recording.2023-12-13.at.7.52.38.PM.mov

ChatMessage (made it more efficient!)

Screen.Recording.2023-12-13.at.7.54.56.PM.mov