Add support for configuring point size in Visualize Lidar GUI plugin

[iche033]

🎉 New feature

depends on gazebosim/gz-rendering#392

Summary

Added a spin box for configuring size of lidar point visualization in Visualize Lidar plugin. Note it only affects Point visualization type. Works for ogre and ogre2 render engine.

Test it

1. Launch an example world with gpu ray sensor, e.g.:

   ign gazebo -v 4 gpu_lidar_sensor.sdf
   

2. Open the Visualize Lidar GUI plugin by going to the top right menu (3 vertical dots), scroll down and click on Visualize Lidar.

3. Unpause the simulation by hitting the play button

4. Refresh the topic drop down list and select the /lidar topic

5. Select Points Visual Type to see the default point visualization with size 1

6. Change Point Size to 5 and hit Enter to see larger points.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[ahcorde]

LGTM, just a minor style fix

[ahcorde]

cpplint is failing. Fixed here #1025

[codecov]

Codecov Report

Merging #1021 (1d7a8f5) into ign-gazebo6 (447e5c2) will decrease coverage by 0.02%.
The diff coverage is n/a.

❗ Current head 1d7a8f5 differs from pull request most recent head b6a379a. Consider uploading reports for the commit b6a379a to get more accurate results

@@               Coverage Diff               @@
##           ign-gazebo6    #1021      +/-   ##
===============================================
- Coverage        64.07%   64.04%   -0.03%     
===============================================
  Files              255      255              
  Lines            20051    20051              
===============================================
- Hits             12847    12841       -6     
- Misses            7204     7210       +6     

Impacted Files	Coverage Δ
src/SimulationRunner.cc	92.91% <0.00%> (-1.02%)	⬇️

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