Should we fork ImGui?

Complaints:

1. For compatibility reasons, ImGui uses C. We are all about modern C++, so make it work with the standard library.
2. Warn if identical names are used. Currently, it will simply not work without any warning.

The issue names ImGui and two broad compatibility and warning goals, but does not identify files, tests, or entry points. First inspect how ImGui is integrated into the renderer and determine the intended scope for standard-library support and duplicate-name diagnostics; done is not defined by the issue.

Written by the indexing model from the issue text.