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

src/sdl_window.h

@@ -58,6 +58,10 @@ public:
         return is_open;
     }
 
+    [[nodiscard]] SDL_Window* GetSdlWindow() const {
+        return window;
+    }
+
     WindowSystemInfo getWindowInfo() const {
         return window_info;
     }