Add SetImguiContext

[sonoro1234]

in implot

// Sets the current ImGui context. This is ONLY necessary if you are compiling
// ImPlot as a DLL (not recommended) separate from your ImGui compilation. It
// sets the global variable GImGui, which is not shared across DLL boundaries.
// See GImGui documentation in imgui.cpp for more details.
IMPLOT_API void SetImGuiContext(ImGuiContext* ctx);