Update shader_prepass, testbed_2d, and first_person_view_model examples to use children! macro

[krunchington]

Objective

Contributes to #18238
Updates the shader_prepass, testbed_2d and first_person_view_model examples to use the children! macro. I wanted to keep the PR small but chose to do 3 examples since they were all limited in scope

Solution

Updates examples to use the Improved Spawning API merged in #17521

Testing

• Did you test these changes? If so, how?
  • Opened the examples before and after and verified the same behavior was observed. I did this on Ubuntu 24.04.2 LTS using --features wayland.
• Are there any parts that need more testing?
  • Other OS's and features can't hurt, but this is such a small change it shouldn't be a problem.
• How can other people (reviewers) test your changes? Is there anything specific they need to know?
  • Run the examples yourself with and without these changes.
• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?
  • see above

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Showcase

n/a

Migration Guide

n/a

[github-actions]

Your PR caused a change in the graphical output of an example or rendering test. This might be intentional, but it could also mean that something broke!
You can review it at https://pixel-eagle.com/project/B04F67C0-C054-4A6F-92EC-F599FEC2FD1D?filter=PR-18270

If it's expected, please add the M-Deliberate-Rendering-Change label.

If this change seems unrelated to your PR, you can consider updating your PR to target the latest main branch, either by rebasing or merging main into it.

[krunchington]

Your PR caused a change in the graphical output of an example or rendering test. This might be intentional, but it could also mean that something broke! You can review it at https://pixel-eagle.com/project/B04F67C0-C054-4A6F-92EC-F599FEC2FD1D?filter=PR-18270

If it's expected, please add the M-Deliberate-Rendering-Change label.

If this change seems unrelated to your PR, you can consider updating your PR to target the latest main branch, either by rebasing or merging main into it.

Hm, when clicking the link here I see a comparison which reports 17 screenshots in the unchanged category. Is there something I'm missing here?
https://pixel-eagle.com/project/b04f67c0-c054-4a6f-92ec-f599fec2fd1d/run/9708/compare/9689

[alice-i-cecile]

Yeah that's really odd. @mockersf, do you know what's up with that?

[krunchington]

I resolved a merge conflict on these lines, I believe this line was the only delta but worth re-reviewing with a close eye.