Ensure that find_package(TinyXML2) defines tinyxml2::tinyxml2 even on case insensitive filesystems

[traversaro]

🦟 Bug fix

Summary

On case-insensitive filesystem, it is possible that FindTinyXML2.cmake is used if the caller invoked find_package(TINYXML2), that is the signature used by tinyxml2_vendor, see https://github.com/ros2/tinyxml2_vendor/blob/b66cece6ed99ba3c3b2b64bc56c0f717dd33243b/cmake/Modules/FindTinyXML2.cmake .

If that is the case (and we detect it by checking the value of CMAKE_FIND_PACKAGE_NAME) we also define a tinyxml2::tinyxml2 target for tinyxml2_vendor compatibility.

This is a sister PR of ros2/tinyxml2_vendor#22 .

Checklist

• Signed all commits for DCO
• Added tests
• 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)
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