Make it easier to subclass components

[philippjfr]

A number of changes to make it easier to subclass component classes:

• ChatFeed and ChatInterface component types can now be set as class variables
• Fix issue falsely detecting a non-instance parameter type as a child
• Fix incorrectly detecting groups on Select widget

These changes are needed for the work on panel-material-ui so I don't have to reimplement entire classes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.08%. Comparing base (8f9cc0f) to head (af9a6fa).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7730      +/-   ##
==========================================
- Coverage   87.08%   87.08%   -0.01%     
==========================================
  Files         346      346              
  Lines       52711    52716       +5     
==========================================
+ Hits        45904    45908       +4     
- Misses       6807     6808       +1     

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