Bump third_party/imgui/repo from 87d7f77 to 2ab3946 (project-chip#40380)

Bumps [third_party/imgui/repo](https://github.com/ocornut/imgui) from `87d7f77` to `2ab3946`.
- [Release notes](https://github.com/ocornut/imgui/releases)
- [Commits](ocornut/imgui@87d7f77...2ab3946)

---
updated-dependencies:
- dependency-name: third_party/imgui/repo
  dependency-version: 2ab3946ecb12962eff96c9bc13ef83d403c84dd8
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]