Factorize input hooks into reusable monitor classes

Those monitors will need some context so this will be useful
in the nearby future.

src/duckstation-qt/inputbindingmonitor.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include "frontend-common/controller_interface.h"
+#include <QtCore/QObject>
+
+// NOTE: Those Monitor classes must be copyable to meet the requirements of std::function, but at the same time we want
+// copies to be opaque to the caling code and share context. Therefore, all mutable context of the monitor (if required)
+// must be enclosed in a std::shared_ptr. m_parent/m_axis_type don't mutate so they don't need to be stored as such.
+
+class InputButtonBindingMonitor
+{
+public:
+  explicit InputButtonBindingMonitor(QObject* parent) : m_parent(parent) {}
+
+  ControllerInterface::Hook::CallbackResult operator()(const ControllerInterface::Hook& ei) const;
+
+private:
+  QObject* m_parent;
+};
+
+class InputAxisBindingMonitor
+{
+public:
+  explicit InputAxisBindingMonitor(QObject* parent, Controller::AxisType axis_type)
+    : m_parent(parent), m_axis_type(axis_type)
+  {
+  }
+
+  ControllerInterface::Hook::CallbackResult operator()(const ControllerInterface::Hook& ei) const;
+
+private:
+  QObject* m_parent;
+  Controller::AxisType m_axis_type;
+};
+
+class InputRumbleBindingMonitor
+{
+public:
+  explicit InputRumbleBindingMonitor(QObject* parent) : m_parent(parent) {}
+
+  ControllerInterface::Hook::CallbackResult operator()(const ControllerInterface::Hook& ei) const;
+
+private:
+  QObject* m_parent;
+};