Enable ImGui for use in Fahrenheit.

[fkelava]

This did not initially work because of missing DX11/Win32 backend enablement.

ImGui.NET does not bundle/wrap the backends, so that is out of the question. We can therefore do two things:

• Write our own that includes them;
• Perform ImGui enablement from C++ and include the imgui_impl_*.h headers verbatim.

[fkelava]

Rough procedure for compiling an amended ImGui.NET/cimgui:

• git clone https://luajit.org/git/luajit.git
• From a Developer PowerShell, run the supplied msvcbuild.bat
• Copy luajit.exe, lua51.dll to some arbitrary folder, and the contents of src/jit to a folder lua/jit in the same place as the former two
• git clone --recursive https://github.com/cimgui/cimgui.git
• In generator/generator.bat, edit the set PATH directive to include your LuaJIT folder
• In generator/generator.bat, have the luajit directive read ./generator.lua cl "internal noimstrv" dx11 win32 %*
• Run generator/generator.bat
• Amend the top-level CMakeLists.txt as such:

  #general settings
  file(GLOB IMGUI_SOURCES
  cimgui.cpp
  imgui/imgui.cpp
  imgui/imgui_draw.cpp
  imgui/imgui_demo.cpp
  imgui/imgui_widgets.cpp
  imgui/backends/imgui_impl_win32.cpp
  imgui/backends/imgui_impl_dx11.cpp
  ${TABLES_SOURCE}
  )

• Open the folder in Visual Studio, select Manage Configurations
• Set the Toolset to msvc_x86_x64, save, then compile
• git clone https://github.com/ImGuiNET/ImGui.NET
• Place the new cimgui.dll in deps/cimgui/win_x86
• In src\CodeGenerator\definitions\cimgui, place cimgui's generator/output/{impl_definitions,definitions,structs_and_enums}.json
• Patch CodeGenerator's ImguiDefinitions.cs according to: https://github.com/equilibrium-hub/ImGui.NET/commit/696c9b7a71a0e8adf19a0f108a1550e0075e41c3#diff-8a4f306bfae678663d6bfafdb3b902f8afe3246a28ccd14e1d3379d22476b152R42-R48, https://github.com/equilibrium-hub/ImGui.NET/commit/696c9b7a71a0e8adf19a0f108a1550e0075e41c3#diff-8a4f306bfae678663d6bfafdb3b902f8afe3246a28ccd14e1d3379d22476b152R108
• Build CodeGenerator, run CodeGenerator, place its output under ImGui.NET's Generated folder
• Build it for x86

[fkelava]

Fahrenheit will bring LuaJIT, cimgui and ImGui.NET in as submodules and provide build scripts as soon as it is confirmed that this, in fact, works.