Use qt6 as the default dependency from rosdep

[ahcorde]

Related with #1634

[ahcorde]

Related PR ros/rosdistro#48855 to bring svg devel package

[luca-della-vedova]

Thanks you for the fix!

For reference, I believe the issue was that we export Qt5 as a dependency and call find_package on it:

$ cat /opt/ros/rolling/share/rviz_common/cmake/ament_cmake_export_dependencies-extras.cmake 
# generated from ament_cmake_export_dependencies/cmake/ament_cmake_export_dependencies-extras.cmake.in

set(_exported_dependencies "geometry_msgs;message_filters;pluginlib;Qt5;rclcpp;rviz_ogre_vendor;rviz_rendering;sensor_msgs;std_msgs;std_srvs;tf2;tf2_ros;yaml_cpp_vendor;yaml-cpp")

But on the other hand we find_package for either Qt6 or Qt5, whichever is found first:

$ cat /opt/ros/rolling/share/rviz_common/cmake/rviz_common-extras.cmake 
# find package Qt5 because otherwise using the rviz_common::rviz_common
# exported target will complain that the Qt5::Widgets target does not exist
find_package(QT NAMES Qt6 Qt5 QUIET COMPONENTS Widgets)
find_package(Qt${QT_VERSION_MAJOR} QUIET COMPONENTS Widgets)

So if Qt6 is installed we end up with a clash where we find both Qt6 and Qt5 and that doesn't really work.
On the other hand, with this PR, the ament_cmake_export_dependencies-extras.cmake becomes the following:

$ cat install/rviz_common/share/rviz_common/cmake/ament_cmake_export_dependencies-extras.cmake 
# generated from ament_cmake_export_dependencies/cmake/ament_cmake_export_dependencies-extras.cmake.in

set(_exported_dependencies "geometry_msgs;message_filters;pluginlib;Qt6;rclcpp;rviz_ogre_vendor;rviz_rendering;sensor_msgs;std_msgs;std_srvs;tf2;tf2_ros;yaml_cpp_vendor;yaml-cpp")

So we will correctly only look for Qt6 (and possibly fallback to Qt5, but I haven't tested that code path).
I wonder if it is an explicit aim to keep supporting Qt5 or not, I haven't tested that path

[ahcorde]

Pulls: #1635
Gist: https://gist.githubusercontent.com/ahcorde/276dbe5df396bdb03ee1f73df82916f5/raw/899c6b81bdd8c422402daf88ae2dac0d8b7a1c91/ros2.repos
BUILD args: --packages-above-and-dependencies rviz2 rviz_common rviz_default_plugins rviz_rendering rviz_rendering_tests rviz_visual_testing_framework
TEST args: --packages-above rviz2 rviz_common rviz_default_plugins rviz_rendering rviz_rendering_tests rviz_visual_testing_framework
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/17698

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[ahcorde]

@ros-pull-request-builder retest this please

[ahcorde]

@ros-pull-request-builder retest this please