Thread safe `cimgui`

[azeno]

The cimgui shipped with the ImGui.NET package is sadly not thread safe (the current internal context is a static field). Did a quick test and it crashed badly. To make it thread safe we need to compile cimgui on our own. Did a quick test and it worked. The steps to build a modified version with a thread static internal context are

• Checkout ImGui.NET-nativebuild
• Add to imconfig.h

  struct ImGuiContext;
  extern thread_local ImGuiContext* MyImGuiTLS;
  #define GImGui MyImGuiTLS

• Add to cimgui_template.cpp after the cimgui include

  thread_local ImGuiContext* MyImGuiTLS;
  #define GImGui MyImGuiTLS

• Regenerate the bindings with generator.bat
• Compile the lib with build-native.cmd

Note: To run the generator you need to extract luajit (from https://luapower.com/luajit) and mingw64 (from https://github.com/niXman/mingw-builds-binaries/releases) and add both their bin folders to the path variable inside the generator.bat file.

In our project we then need to exclude the native asset with ExcludeAssets="native" on the ImGui.NET package reference and include the custom built one.

[azeno]

Fixed by 9a96aeeed86e252ae7f9fb875bd964cbb2811a48