Implement Widget.from_values

[philippjfr]

Implements #6071

• Add docs
• Update examples
• Add tests

[codecov]

Codecov Report

Attention: Patch coverage is 31.81818% with 15 lines in your changes missing coverage. Please review.

Project coverage is 81.77%. Comparing base (78982fb) to head (7387b62).
Report is 1 commits behind head on main.

Files	Patch %	Lines
panel/widgets/base.py	37.50%	10 Missing ⚠️
panel/util/__init__.py	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7033      +/-   ##
==========================================
- Coverage   82.22%   81.77%   -0.46%     
==========================================
  Files         326      326              
  Lines       48271    48293      +22     
==========================================
- Hits        39691    39491     -200     
- Misses       8580     8802     +222     

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[jbednar]

This is a good start towards #7003; thanks! A few questions:

1. What starting value is used by default? Seems like you'd want a midpoint value by default, not just the start value?
2. For a Pandas Series, it should be cheap to calculate the min, avg, and max in a single pass (e.g. df['column_name'].agg(['min', 'average', 'max'])) to get the start, value, and end; is that a useful special case for a Series?
3. Range widgets seem like they'd need different behavior, since a range should normally default to the start and end of the range. Will that already happen automatically?