Helper to get version number from package.xml

[scpeters]

🎉 New feature

Follow-up to gazebosim/gz-math#639, part of gazebosim/sdformat#1491

Summary

This adds a python script and a cmake helper function for getting the version number from a package.xml file.

Test it

Test using the version_from_package_xml example.

1. Build and install gz-cmake from this branch
2. cd examples/version_from_package_xml
3. mkdir build && cd build
4. cmake ..
5. You should see the following lines in the console output, pulling the version number from the example package.xml file

-- PACKAGE_XML_VERSION 8.21.65
-- PACKAGE_XML_VERSION_MAJOR 8
-- PACKAGE_XML_VERSION_MINOR 21
-- PACKAGE_XML_VERSION_PATCH 65
-- gz-version_from_package_xml version 8.21.65

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.

[j-rivero]

Made some cosmetic commits, one suggestion and one real fix.

Thanks for the PR!

[j-rivero]

Good to go with green CI ! Thanks!