qt/hotkey: Get rid of global hotkey map instance

Instead, we make a proper registry class and house it within the main
window, then pass it to whatever needs access to the loaded hotkeys.

This way, we avoid a global variable, and don't need to initialize a
std::map instance before the program can do anything.

src/citra_qt/main.h

@@ -9,6 +9,7 @@
 #include <QMainWindow>
 #include <QTimer>
 #include <QTranslator>
+#include "citra_qt/hotkeys.h"
 #include "common/announce_multiplayer_room.h"
 #include "core/core.h"
 #include "core/hle/service/am/am.h"
@@ -237,6 +238,8 @@ private:
     // stores default icon theme search paths for the platform
     QStringList default_theme_paths;
 
+    HotkeyRegistry hotkey_registry;
+
 protected:
     void dropEvent(QDropEvent* event) override;
     void dragEnterEvent(QDragEnterEvent* event) override;