Fix grouping of skeletons by constraints

[jslee02]

• Apply Fix grouping of contact constraints #1624 for other constraints
• Fix compile warnings with GCC 11.2

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[codecov]

Codecov Report

Merging #1628 (9637b02) into main (6f9feed) will decrease coverage by 0.00%.
The diff coverage is 36.36%.

@@            Coverage Diff             @@
##             main    #1628      +/-   ##
==========================================
- Coverage   58.92%   58.91%   -0.01%     
==========================================
  Files         477      477              
  Lines       40178    40178              
==========================================
- Hits        23673    23670       -3     
- Misses      16505    16508       +3     

Impacted Files	Coverage Δ
dart/constraint/JointLimitConstraint.cpp	0.00% <0.00%> (ø)
dart/constraint/ServoMotorConstraint.cpp	0.00% <0.00%> (ø)
dart/constraint/SoftContactConstraint.cpp	0.00% <0.00%> (ø)
dart/constraint/WeldJointConstraint.cpp	6.59% <0.00%> (ø)
dart/dynamics/detail/DegreeOfFreedomPtr.hpp	85.07% <ø> (ø)
dart/constraint/BallJointConstraint.cpp	67.61% <50.00%> (ø)
dart/constraint/JointConstraint.cpp	73.58% <100.00%> (ø)
dart/constraint/JointCoulombFrictionConstraint.cpp	82.45% <100.00%> (ø)
dart/constraint/MimicMotorConstraint.cpp	80.32% <100.00%> (ø)
dart/dynamics/EulerJoint.cpp	70.17% <0.00%> (-2.93%)	⬇️
... and 1 more