Add ptr definitions for TimeParameterization classes

[v4hn]

These were not there before the polymorphy change either,
but they become a bit more important with it.

@rhaschke

[rhaschke]

You beat me pushing this commit. Thanks anyway!

[codecov]

Codecov Report

Merging #3078 (90fd119) into master (6f7ce13) will decrease coverage by 0.03%.
The diff coverage is n/a.

❗ Current head 90fd119 differs from pull request most recent head 85a45b4. Consider uploading reports for the commit 85a45b4 to get more accurate results

@@            Coverage Diff             @@
##           master    #3078      +/-   ##
==========================================
- Coverage   61.70%   61.68%   -0.02%     
==========================================
  Files         374      374              
  Lines       33258    33258              
==========================================
- Hits        20520    20511       -9     
- Misses      12738    12747       +9     

Impacted Files	Coverage Δ
...ctory_processing/iterative_time_parameterization.h	100.00% <ø> (ø)
...ry_processing/time_optimal_trajectory_generation.h	100.00% <ø> (ø)
...veit/trajectory_processing/time_parameterization.h	100.00% <ø> (ø)
...eit_ros/manipulation/pick_place/src/pick_place.cpp	88.58% <0.00%> (-3.80%)	⬇️
...ipulation/pick_place/src/manipulation_pipeline.cpp	71.91% <0.00%> (-2.47%)	⬇️
..._interface/src/detail/constrained_goal_sampler.cpp	74.51% <0.00%> (-1.96%)	⬇️
...g_scene_interface/src/planning_scene_interface.cpp	51.10% <0.00%> (-1.09%)	⬇️
...nning_scene_monitor/src/planning_scene_monitor.cpp	66.88% <0.00%> (+0.13%)	⬆️

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[rhaschke]

I will prepare a patch release over the weekend. Hence, please disregard/drop my additional commit before merging.
Background: there is a regression fix (#3076) that should be released anyway.