Improve robustness of calculate_variable_from_constraint()

[jsiirola]

Fixes # .

Summary/Motivation:

#2806 accidentally changed the exception type expected when converting an expression to sympy fails (from TypeError to ValueError). This changes the exception back to TypeError.

In addition, this adds behavior to calculate_variable_from_constraint() so that if the user does not specify a specific differentiation method and symbolic differentiation with sympy fails, then it will (nearly silently) fall back on numeric differentiation. This resolves user experience issues encountered with tools that wrap calculate_variable_from_constraint() like solve_strongly_connected_components() (see, e.g., https://github.com/IDAES/idaes-pse/pull/1170/files#r1170267327).

Changes proposed in this PR:

• revert change to exception type when converting ExternalFunction expression objects to sympy
• calculate_variable_from_constraint(): implicitly fall back on numeric differentiation when symbolic differentiation fails and no differentiation mode was explicitly set

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03 🎉

Comparison is base (21821ac) 87.14% compared to head (5bf0f1d) 87.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2812      +/-   ##
==========================================
+ Coverage   87.14%   87.17%   +0.03%     
==========================================
  Files         764      764              
  Lines       88262    88270       +8     
==========================================
+ Hits        76914    76949      +35     
+ Misses      11348    11321      -27     

Flag	Coverage Δ
linux	84.23% <100.00%> (+0.04%)	⬆️
osx	73.86% <100.00%> (+<0.01%)	⬆️
other	84.40% <100.00%> (+0.07%)	⬆️
win	81.77% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
pyomo/core/expr/sympy_tools.py	98.98% <100.00%> (+1.01%)	⬆️
pyomo/util/calc_var_value.py	100.00% <100.00%> (ø)

... and 12 files with indirect coverage changes

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