Update imgui and fix missing backends in the cimgui.dll

[jroweboy]

See also the related submodule prs for cimgui https://github.com/Sewer56/cimgui/pull/1 and DearImGuiSharp-NativeBuild https://github.com/Sewer56/DearImGuiSharp-NativeBuilds/pull/1

Changes

Updates Imgui bindings to the latest 1.89.3 and fixes issues with msvc builds for extra backends. In the current library, the bindings include the bindings for backends such as GLFW but they are actually not present in the dll. (This took me way too long to figure out :P)

Note

I didn't update the Linux or MacOS as 1) i don't have the build environments for them setup 2) they don't use these platform backends anyway

Screenshots

Below: DLL export listing for the current x86 cimgui.dll

After this PR, they are now present in the dll