Improve particle scattering noise

[iche033]

🦟 Bug fix

Summary

Applies more uniform random scattering based on size of the particle emitter region (instead of the first particle hit)

Affects depth, rgbd, and gpu_rays sensors

To test

You can test with ign gazebo using this sensor_particles_scattering.sdf world

ign gazebo -v 4 -r sensor_particles_scattering.sdf

You can see the lidar visualization by using the Visualize Lidar plugin. Top Right menu -> Visualize Lidar

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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