RobotecSplineTools: add rclcpp dependency

[jhanca-robotecai]

What does this PR do?

We use ROS 2 in the gem, but we do not explicitly link to rclcpp and nav_msgs. The linking is done via ROS 2 Gem. However, it does not work in some cases, resulting in an error which is hard to decrypt:

CMake Error in /workspace/project/perception-simulation/gems/robotec-o3de-tools/Gems/RobotecSplineTools/Code/CMakeLists.txt:
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  Error evaluating generator expression:
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    $<TARGET_PROPERTY:fastcdr,TYPE>
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  Target "fastcdr" not found.

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How was this PR tested?

Successfully builds.

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Screenshots / Logs / Supporting Evidence (if applicable)

Add screenshots, terminal logs, or relevant links to builds/tests as needed.

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Committer Checklist

Please confirm the following before marking this PR as ready for review:

• Code changes are well-documented
• Tests have been added or updated
• Code owners file and CI config were updated if new Gem was added
• The code is formatted according to the project's style guide
• The version number has been updated according to the contributing guidelines