Update log_layers_ecs example for children macro

[krunchington]

Objective

Contributes to #18238
Updates the log_layers_ecs, example to use the children! macro.

Note that I did not use a macro, nor Children::spawn for the outer layer. Since the EventReader is borrowed mutably, any .map I did on events.read() was going to have the reference outlive the function body. I believe this scope of change is correct for the PR.

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

[krunchington]

The more I look at trying to make the outer spawniter work, the more I feel like the submitted changes are the right scope, especially since we reverted the spawniter changes in other related PRs. I think this is ready for straightforward review. Editing PR description to remove the extra context.