Update ImGui 1.86-docking

[forkercat]

Description

This is to update ImGui in docking branch to 1.86.

Please refer to the previous pull request #7. Changes are the same.

Checklist

• I've read the Contribution Guidelines
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (to the extent possible).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexpected benchmark regressions.
• I've updated the documentation (if appropriate).