Use Qt6 on Rolling and newer distros

[nbbrooks]

Description

Rviz switchd to Qt6 in version 15.1 ros2/rviz#1635

As we support the latest features in main being source built to non-EOL distros, the following cases must be supported

• Humble (Ubuntu 22.04): Use Qt5
• Jazzy (Ubuntu 24.04): Use Qt5
• Kilted (Ubuntu 24.04): Use Qt5
• Rolling (currently Ubuntu 42.04): Use Qt6

There are some specific checks in here to handle cases where Qt5 and Qt6 are installed.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.22%. Comparing base (f1135a4) to head (687f30f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...plugin/src/motion_planning_frame_joints_widget.cpp	0.00%	2 Missing ⚠️
...eit_setup_framework/src/xml_syntax_highlighter.cpp	0.00%	2 Missing ⚠️
..._setup_srdf_plugins/src/collision_linear_model.cpp	0.00%	2 Missing ⚠️
..._setup_srdf_plugins/src/collision_matrix_model.cpp	0.00%	2 Missing ⚠️
...tup_srdf_plugins/src/default_collisions_widget.cpp	0.00%	2 Missing ⚠️
...planning_rviz_plugin/src/motion_planning_frame.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            main    #3707       +/-   ##
==========================================
+ Coverage   0.00%   46.22%   +46.22%     
==========================================
  Files        539      726      +187     
  Lines      47592    59497    +11905     
  Branches    6085     7624     +1539     
==========================================
+ Hits           0    27499    +27499     
+ Misses     47592    31832    -15760     
- Partials       0      166      +166     

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[nbbrooks]

The [CI / rolling-ci + ikfast + clang-tidy](https://github.com/moveit/moveit2/actions/runs/23422946195/job/68131764804?pr=3707) failure appears unrelated to the Qt5/Qt6 issues that are present on main.