[ros2] Export tinyxml2 directly from pluginlib-extras.cmake (#192)

* [ros2] Export tinyxml2 directly from pluginlib-extras.cmake

* use imported instead.

Author: seanyen

pluginlib/pluginlib-extras.cmake

@@ -45,7 +45,7 @@ find_package(tinyxml2_vendor REQUIRED)
 find_package(TinyXML2 REQUIRED)
 list(APPEND pluginlib_LIBRARIES ${TinyXML2_LIBRARIES})
 
-add_library(tinyxml2_vendor INTERFACE)
+add_library(tinyxml2_vendor INTERFACE IMPORTED)
 target_include_directories(tinyxml2_vendor INTERFACE
   ${TinyXML2_INCLUDE_DIRS})
 target_link_libraries(tinyxml2_vendor INTERFACE