Dear ImGui Implementation (#598)

* added imgui as dependency

* imgui renderer/basic input implementation

* imgui: add layers system

Add video info layer to show fps. Press F10 to toggle it.

* imgui: add custom imgui config

* imgui: gamepad capture, stopping propagation

* imgui: changed config & log file path to use portable dir

* videoout: render blank frame when video output is closed

required to render imgui even when game has no video output

- fixed merge compile-error

externals/CMakeLists.txt

@@ -155,6 +155,17 @@ if (APPLE)
     endif()
 endif()
 
+# Dear ImGui
+add_library(Dear_ImGui
+        dear_imgui/imgui.cpp
+        dear_imgui/imgui_demo.cpp
+        dear_imgui/imgui_draw.cpp
+        dear_imgui/imgui_internal.h
+        dear_imgui/imgui_tables.cpp
+        dear_imgui/imgui_widgets.cpp
+)
+target_include_directories(Dear_ImGui INTERFACE dear_imgui/)
+
 # Tracy
 option(TRACY_ENABLE "" ON)
 option(TRACY_NO_CRASH_HANDLER "" ON) # Otherwise texture cache exceptions will be treaten as a crash