QtGui: Handle file open events

Handle file open events received by Dolphin. This allows Wii/GC files to be
opened when double-clicked or dropped on the Dolphin application on macOS.

Source/Core/DolphinQt/QtUtils/FileOpenEventFilter.cpp

@@ -0,0 +1,24 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include <QFileOpenEvent>
+
+#include "DolphinQt/QtUtils/FileOpenEventFilter.h"
+
+FileOpenEventFilter::FileOpenEventFilter(QObject* event_source) : QObject(event_source)
+{
+  event_source->installEventFilter(this);
+}
+
+bool FileOpenEventFilter::eventFilter(QObject* object, QEvent* event)
+{
+  if (event->type() == QEvent::FileOpen)
+  {
+    auto* openEvent = static_cast<QFileOpenEvent*>(event);
+    emit fileOpened(openEvent->file());
+    return true;
+  }
+
+  return false;
+}

Source/Core/DolphinQt/QtUtils/FileOpenEventFilter.h

@@ -0,0 +1,20 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <QObject>
+
+class FileOpenEventFilter : public QObject
+{
+  Q_OBJECT
+public:
+  explicit FileOpenEventFilter(QObject* event_source);
+
+signals:
+  void fileOpened(const QString& file_name);
+
+private:
+  bool eventFilter(QObject* object, QEvent* event) override;
+};