Improvements to the ReactiveExpr reference guide

[MarcSkovMadsen]

I had problems understanding the new ReactiveExpr pane from the reference guide. Especially how to layout things.

During that process I discovered that one of the problems is that default_layout is mentioned in the reference guide. And it should not be. See #5948. This PR will be Closing #5948 .

I added more small examples to help the user understand what reactive expressions are and how powerful they can be.

I added in emojis. I know some people think its too much. But I just think they communicate better when you open up the notebook during a training session, a conference talk or if you record a video for social media. I also believe that users when studying the notebook feel its more fun and engaging to study. For the same reason I used the material design.

Todo

• Fix the bug ReactiveExpr - Styled DataFrame Example is broken #5958. I don't plan to do this. I hope Phillip will.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (905cf91) 82.54% compared to head (8c5c123) 84.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5960      +/-   ##
==========================================
+ Coverage   82.54%   84.32%   +1.78%     
==========================================
  Files         291      291              
  Lines       43348    43348              
==========================================
+ Hits        35781    36555     +774     
+ Misses       7567     6793     -774     

Flag	Coverage Δ
ui-tests	40.89% <100.00%> (+2.42%)	⬆️
unitexamples-tests	72.39% <100.00%> (+0.24%)	⬆️

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[MarcSkovMadsen]

Assets

Here is a little bit for the social media

param-rx-examples.mp4

param-reactive-expressions-layout.mp4

panel-reactive-expression-reference-example.mp4

[philippjfr]

Looks good!