Make ignition-physics CMake config files relocatable

[traversaro]

🦟 Bug fix

Summary

Avoid to use EIGEN3_INCLUDE_DIRS variable with target_include_directories command, as this result in hardcoding the EIGEN3_INCLUDE_DIRS value in the ignition-physics build machine, that could be different from the location where the Eigen3 include directories are installed in the machine that is consuming the ignition-physics CMake package.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

Merging #282 (09b0d0a) into ign-physics4 (34dbb87) will not change coverage.
The diff coverage is n/a.

❗ Current head 09b0d0a differs from pull request most recent head c98a8dd. Consider uploading reports for the commit c98a8dd to get more accurate results

@@              Coverage Diff              @@
##           ign-physics4     #282   +/-   ##
=============================================
  Coverage         75.75%   75.75%           
=============================================
  Files               125      125           
  Lines              5503     5503           
=============================================
  Hits               4169     4169           
  Misses             1334     1334           

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[traversaro]

(I will fix DCO tommorow morning in CEST time zone)