Add default constructor to RayHit

[jslee02]

Necessary to initialize the members. Also, RayHit.mHasHit is removed since it's not used.

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[codecov]

Codecov Report

Merging #1345 into release-6.9 will decrease coverage by <.01%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           release-6.9    #1345      +/-   ##
===============================================
- Coverage        56.89%   56.89%   -0.01%     
===============================================
  Files              366      366              
  Lines            27174    27177       +3     
===============================================
  Hits             15461    15461              
- Misses           11713    11716       +3

Impacted Files	Coverage Δ
dart/collision/RaycastResult.hpp	100% <ø> (ø)	⬆️
dart/collision/RaycastResult.cpp	100% <100%> (ø)	⬆️
dart/dynamics/Skeleton.cpp	65.95% <0%> (-0.17%)	⬇️