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_general.h

@@ -7,6 +7,8 @@
 #include <memory>
 #include <QWidget>
 
+class HotkeyRegistry;
+
 namespace Ui {
 class ConfigureGeneral;
 }
@@ -18,6 +20,7 @@ public:
     explicit ConfigureGeneral(QWidget* parent = nullptr);
     ~ConfigureGeneral();
 
+    void PopulateHotkeyList(const HotkeyRegistry& registry);
     void applyConfiguration();
     void retranslateUi();
 
@@ -30,6 +33,5 @@ signals:
 private:
     void setConfiguration();
 
-private:
     std::unique_ptr<Ui::ConfigureGeneral> ui;
 };