build(deps): Bump external/imgui from 947aa9c to eb642a9

Bumps [external/imgui](https://github.com/ocornut/imgui) from `947aa9c` to `eb642a9`.
- [Release notes](https://github.com/ocornut/imgui/releases)
- [Commits](ocornut/imgui@947aa9c...eb642a9)

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

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