Imgui update

[Moniz]

There's also some issues in imgui.cpp and implot.cpp with some platforms, but I've broken this out into a separate PR in case you don't want to make changes to the imgui files directly

[ocornut]

@Moniz about the imgui.cpp specific commits aka 1bb9374

I believe it is unnecessary, the correct change would be that for whatever platform (e.g. PS5 or whatever) which doesn't have those functions you can use #define IMGUI_DISABLE_DEFAULT_SHELL_FUNCTIONS, which is typically set in your imconfig file.
I am open to adding extra logic to define IMGUI_DISABLE_DEFAULT_SHELL_FUNCTIONS by default on certain platforms, you can privately email me with details and we can figure out the suitable ifdef.