Bump third_party/imgui/repo from fbf45ad to 3c435c0 (project-chip#32528)

Bumps [third_party/imgui/repo](https://github.com/ocornut/imgui) from `fbf45ad` to `3c435c0`.
- [Release notes](https://github.com/ocornut/imgui/releases)
- [Commits](ocornut/imgui@fbf45ad...3c435c0)

---
updated-dependencies:
- dependency-name: third_party/imgui/repo
  dependency-type: direct:production
...

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