Make the FIFO Player a separate window

This way, it can be focused with the render window behind it, instead of having the main window show up and cover the render window.  This is useful for adjusting the object range, among other things.

Source/Core/DolphinQt/MainWindow.cpp

@@ -1214,7 +1214,7 @@ void MainWindow::ShowFIFOPlayer()
 {
   if (!m_fifo_window)
   {
-    m_fifo_window = new FIFOPlayerWindow(this);
+    m_fifo_window = new FIFOPlayerWindow;
     connect(m_fifo_window, &FIFOPlayerWindow::LoadFIFORequested, this,
             [this](const QString& path) { StartGame(path, ScanForSecondDisc::No); });
   }