Introduce ControllerInterface class, port SDL interface over

This breaks controller support in the SDL frontend until it's ported
over to the common interface.

src/frontend-common/controller_interface.cpp

@@ -0,0 +1,93 @@
+#include "controller_interface.h"
+#include "common/assert.h"
+#include "common/log.h"
+#include "core/controller.h"
+#include "core/system.h"
+#include <cmath>
+Log_SetChannel(ControllerInterface);
+
+ControllerInterface::ControllerInterface() = default;
+
+ControllerInterface::~ControllerInterface() = default;
+
+bool ControllerInterface::Initialize(CommonHostInterface* host_interface)
+{
+  m_host_interface = host_interface;
+  return true;
+}
+
+void ControllerInterface::Shutdown()
+{
+  m_host_interface = nullptr;
+}
+
+System* ControllerInterface::GetSystem() const
+{
+  return m_host_interface->GetSystem();
+}
+
+Controller* ControllerInterface::GetController(u32 slot) const
+{
+  System* system = GetSystem();
+  return system ? system->GetController(slot) : nullptr;
+}
+
+void ControllerInterface::SetHook(Hook::Callback callback)
+{
+  std::unique_lock<std::mutex> lock(m_event_intercept_mutex);
+  Assert(!m_event_intercept_callback);
+  m_event_intercept_callback = std::move(callback);
+}
+
+void ControllerInterface::ClearHook()
+{
+  std::unique_lock<std::mutex> lock(m_event_intercept_mutex);
+  if (m_event_intercept_callback)
+    m_event_intercept_callback = {};
+}
+
+bool ControllerInterface::DoEventHook(Hook::Type type, int controller_index, int button_or_axis_number, float value)
+{
+  std::unique_lock<std::mutex> lock(m_event_intercept_mutex);
+  if (!m_event_intercept_callback)
+    return false;
+
+  const Hook ei{type, controller_index, button_or_axis_number, value};
+  const Hook::CallbackResult action = m_event_intercept_callback(ei);
+  if (action == Hook::CallbackResult::StopMonitoring)
+    m_event_intercept_callback = {};
+
+  return true;
+}
+
+void ControllerInterface::OnControllerConnected(int host_id)
+{
+  Log_InfoPrintf("Host controller %d connected, updating input map", host_id);
+  m_host_interface->UpdateInputMap();
+}
+
+void ControllerInterface::OnControllerDisconnected(int host_id)
+{
+  Log_InfoPrintf("Host controller %d disconnected, updating input map", host_id);
+  m_host_interface->UpdateInputMap();
+}
+
+void ControllerInterface::ClearBindings() {}
+
+bool ControllerInterface::BindControllerAxis(int controller_index, int axis_number, AxisCallback callback)
+{
+  return false;
+}
+
+bool ControllerInterface::BindControllerButton(int controller_index, int button_number, ButtonCallback callback)
+{
+  return false;
+}
+
+bool ControllerInterface::BindControllerAxisToButton(int controller_index, int axis_number, bool direction,
+                                                     ButtonCallback callback)
+{
+  return false;
+}
+
+void ControllerInterface::UpdateControllerRumble() {}