Pose3: deprecate - and -= operators

[scpeters]

🎉 New feature

Part of #60.

Summary

As noted in gz-math#60, there are concerns about the pose subtraction operator. Given that it is equivalent to multiplying by an inverse (albeit with reversed order A - B = B.Inverse() * A), this deprecates the unitary negation operator - and the subtraction operators - and -=.

This is a draft PR until all usage of the deprecated behavior has been replaced in downstream repositories.

Test it

Run UNIT_Pose3_TEST

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #438 (ae2e1c5) into main (b250500) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #438   +/-   ##
=======================================
  Coverage   99.69%   99.69%           
=======================================
  Files          73       73           
  Lines        6588     6588           
=======================================
  Hits         6568     6568           
  Misses         20       20           

Impacted Files	Coverage Δ
include/gz/math/Pose3.hh	100.00% <100.00%> (ø)

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