Avoid collision checking between objects from the same body node

[pchorak]

I noticed that if I create multiple collision objects for a single link in Gazebo while using DART physics, they are collision checked against each other even though they are part of the same link (body node). The proposed change to CollisionFilter::needCollision prevents collision checking between shapes attached to the same body node.

See collisions.world for an example in Gazebo. It contains a model with two links and self-collisions enabled. The top link consists of two flush collision meshes. Without the change, contacts points (blue dots) are detected between the flush meshes.

With the change, no such contacts are detected.

[codecov]

Codecov Report

Merging #894 into master will increase coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #894      +/-   ##
==========================================
+ Coverage   50.61%   50.63%   +0.01%     
==========================================
  Files         299      299              
  Lines       23409    23411       +2     
  Branches     3015     3016       +1     
==========================================
+ Hits        11849    11854       +5     
+ Misses      10230    10226       -4     
- Partials     1330     1331       +1

Impacted Files	Coverage Δ
dart/collision/CollisionFilter.cpp	51.85% <50%> (-0.15%)	⬇️
dart/dynamics/ShapeNode.cpp	58.62% <0%> (+6.89%)	⬆️