Merging initial integration of NetImgui by Sammyfreg:
- Integration of the NetImgui.
- Build as part of the ImGui module.
- Implemented UE4 sockets.
- Added mirroring and dual context support.
- Menu bar to switch between contexts.

Merging Bugfix for NetImGui: Making sure sockets are all closed before exiting netImgui shutdown.

* Added support for netImgui.
TODO: fix issue with editor not drawing until PIE activated once
TODO: Implement UE4 sockets (instead of using Winsock directly)
TODO: Figure out how to expose options to user, and netImgui server exe

* netImgui: Fix compile and running error in game mode

* NetImgui: Added mirroring option

* Fix for Texture format detection and disconnect request

* Added : Dual Draw support
Added: IsRemoteDrawing() and IsRemoteConnected() to FImGuiModuleProperties
Removed : Intrusive code in FProxyContext
Fixed: NoUnityBuild

* Added support of Unreal Sockets instead of using Windows code. Every platform supported by Unreal should now work with remote connection.

* Changed context index mapping to fix issues with multi-PIE debugging in 4.25.

* Status update with information about NetImgui.

* Bugfix: making sure sockets are all closed before exiting netImgui shutdown

* Fixed Linux crash caused by wrong mapping of key codes.

* Update DearImgui 1.80, NetImgui 1.3

Updating DearImgui and NetImgui libraries to latest version.

* Missing ImGui context release

* Prevent crash while cooking

* Case sensitive include fix

Co-authored-by: Sebastian <sebastian.e.gross@gmail.com>

# Conflicts:
#	CHANGES.md
#	ImGui.uplugin
#	README.md
#	Source/ImGui/ImGui.Build.cs
#	Source/ImGui/Private/ImGuiContextManager.cpp
#	Source/ImGui/Private/ImGuiContextProxy.cpp
#	Source/ImGui/Private/ImGuiDrawData.cpp
#	Source/ThirdParty/ImGuiLibrary/Include/imconfig.h
#	Source/ThirdParty/ImGuiLibrary/Include/imgui.h
#	Source/ThirdParty/ImGuiLibrary/LICENSE.txt
#	Source/ThirdParty/ImGuiLibrary/Private/imgui.cpp
#	Source/ThirdParty/ImGuiLibrary/Private/imgui_demo.cpp
#	Source/ThirdParty/ImGuiLibrary/Private/imgui_draw.cpp
#	Source/ThirdParty/ImGuiLibrary/Private/imgui_internal.h
#	Source/ThirdParty/ImGuiLibrary/Private/imgui_tables.cpp
#	Source/ThirdParty/ImGuiLibrary/Private/imgui_widgets.cpp
#	Source/ThirdParty/ImGuiLibrary/Private/imstb_truetype.h