Lock the Bullet collision environment, for thread safety

[v4hn]

Replaces #2481 and adds minor refinements.

Please review and merge @AndyZe. You disabled maintainer-pushes to your fork, so I had to create a new pull-request.

[codecov]

Codecov Report

Merging #2598 (e4ab2a1) into master (90e70a5) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2598      +/-   ##
==========================================
- Coverage   60.54%   60.50%   -0.04%     
==========================================
  Files         402      402              
  Lines       29606    29543      -63     
==========================================
- Hits        17922    17871      -51     
+ Misses      11684    11672      -12     

Impacted Files	Coverage Δ
.../collision_detection_bullet/collision_env_bullet.h	100.00% <ø> (ø)
...sion_detection_bullet/src/collision_env_bullet.cpp	78.03% <100.00%> (-1.19%)	⬇️
...on/pick_place/src/approach_and_translate_stage.cpp	73.24% <0.00%> (-0.70%)	⬇️
...meterization/work_space/pose_model_state_space.cpp	83.34% <0.00%> (-0.64%)	⬇️
...dl_kinematics_plugin/src/kdl_kinematics_plugin.cpp	81.00% <0.00%> (-0.41%)	⬇️
.../move_group_interface/src/move_group_interface.cpp	47.12% <0.00%> (-0.19%)	⬇️
...nning_scene_monitor/src/planning_scene_monitor.cpp	68.68% <0.00%> (-0.13%)	⬇️
.../ompl_interface/src/detail/constrained_sampler.cpp	59.46% <0.00%> (+16.22%)	⬆️

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[AndyZe]

You disabled maintainer-pushes to your fork, so I had to create a new pull-request.

Sorry for the inconvenience

[v4hn]

Thank you for patching the issue @AndyZe