Add type property to constraint classes

[jslee02]

---

Before creating a pull request

• Document new methods and classes
• Format new code files using clang-format

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change

[codecov]

Codecov Report

Merging #1415 into master will decrease coverage by 0.09%.
The diff coverage is 17.85%.

@@            Coverage Diff            @@
##           master    #1415     +/-   ##
=========================================
- Coverage   57.31%   57.22%   -0.1%     
=========================================
  Files         367      367             
  Lines       27521    27568     +47     
=========================================
+ Hits        15774    15775      +1     
- Misses      11747    11793     +46

Impacted Files	Coverage Δ
dart/constraint/BallJointConstraint.hpp	0% <ø> (ø)	⬆️
dart/constraint/WeldJointConstraint.hpp	0% <ø> (ø)	⬆️
dart/constraint/ContactConstraint.hpp	100% <ø> (ø)	⬆️
dart/constraint/JointLimitConstraint.hpp	100% <ø> (ø)	⬆️
dart/constraint/JointLimitConstraint.cpp	69.69% <0%> (-1.81%)	⬇️
dart/constraint/ServoMotorConstraint.cpp	78.94% <0%> (-3.63%)	⬇️
dart/constraint/MimicMotorConstraint.cpp	80.32% <0%> (-3.44%)	⬇️
dart/constraint/BallJointConstraint.cpp	9.19% <0%> (-0.28%)	⬇️
dart/constraint/SoftContactConstraint.cpp	0% <0%> (ø)	⬆️
dart/constraint/JointCoulombFrictionConstraint.cpp	81.57% <0%> (-3.75%)	⬇️
... and 4 more