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/configuration/configure_dialog.h

@@ -7,6 +7,8 @@
 #include <memory>
 #include <QDialog>
 
+class HotkeyRegistry;
+
 namespace Ui {
 class ConfigureDialog;
 }
@@ -15,7 +17,7 @@ class ConfigureDialog : public QDialog {
     Q_OBJECT
 
 public:
-    explicit ConfigureDialog(QWidget* parent);
+    explicit ConfigureDialog(QWidget* parent, const HotkeyRegistry& registry);
     ~ConfigureDialog();
 
     void applyConfiguration();