core: Move emu_window and key_map into core

* Removes circular dependences (common should not depend on core)

src/citra/emu_window/emu_window_sdl2.cpp

@@ -9,10 +9,10 @@
 #include <SDL.h>
 #include <glad/glad.h>
 #include "citra/emu_window/emu_window_sdl2.h"
-#include "common/key_map.h"
 #include "common/logging/log.h"
 #include "common/scm_rev.h"
 #include "common/string_util.h"
+#include "core/frontend/key_map.h"
 #include "core/hle/service/hid/hid.h"
 #include "core/settings.h"
 #include "video_core/video_core.h"

src/citra/emu_window/emu_window_sdl2.h

@@ -5,7 +5,7 @@
 #pragma once
 
 #include <utility>
-#include "common/emu_window.h"
+#include "core/frontend/emu_window.h"
 
 struct SDL_Window;