Install moveit_core headers within additional moveit_core directory

[ChrisThrasher]

Description

I changed where headers get installed to fix issues with building MoveIt from source when another copy is already installed. By installing all headers inside a moveit_core directory, we add an extra layer of indirection that ensures we know what headers are getting used at any given time.

While I was at it, I also made sure to stop using include_directories inside moveit_core. CMake best practices are to avoid using include_directories, particularly in large projects like this because it makes it difficult to understand what targets have access to what include directories. Removing them from moveit_core makes it easier for us to know what headers we need to install plus it revealed an issue where kinematics_base and robot_model depended on each other. This makes me wonder if perhaps moveit_core should be consolidated into fewer targets.

[tylerjw]

Awesome, thank you @ChrisThrasher.

Here is the link to the colcon docs that justify some of this change: https://colcon.readthedocs.io/en/released/user/overriding-packages.html#how-to-make-it-easier-for-your-users-to-override

[codecov]

Codecov Report

Base: 50.90% // Head: 50.89% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (267dc5e) compared to base (5846106).
Patch has no changes to coverable lines.

❗ Current head 267dc5e differs from pull request most recent head cc32e09. Consider uploading reports for the commit cc32e09 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1785      +/-   ##
==========================================
- Coverage   50.90%   50.89%   -0.00%     
==========================================
  Files         378      378              
  Lines       31728    31728              
==========================================
- Hits        16148    16145       -3     
- Misses      15580    15583       +3     

Impacted Files	Coverage Δ
...nning_scene_monitor/src/planning_scene_monitor.cpp	45.26% <0.00%> (-0.43%)	⬇️
moveit_core/robot_state/src/robot_state.cpp	47.95% <0.00%> (+0.08%)	⬆️

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[vatanaksoytezer]

Looks good to me, thank you for doing this Chris!