[ros2] tinyxml2_vendor not in export set

[Karsten1987]

When trying to export targets which depend on pluginlib, CMake complains that tinyxml2_vendor is not part of any export set.
I've seen this independent from each other within rosbag2 and image_transport.

Starting >>> image_transport
--- stderr: image_transport
CMake Error: install(EXPORT "image_transport" ...) includes target "image_transport" which requires target "tinyxml2_vendor" that is not in any export set.
CMake Generate step failed.  Build files cannot be regenerated correctly.
make: *** [cmake_check_build_system] Error 1
---
Failed   <<< image_transport	[ Exited with code 2 ]

Does it make sense to export the vendor package in the first place? I mean, it makes sense for pluginlib to use the vendor package to link correctly to tinyxml2, but I am not seeing any reason ad-hoc to also export the vendor package if the pluginlib target transitively links correctly against tinyxml2.