QTouchEvent forward declaration; add comment to TouchBegin that was lost in an edit

src/citra_qt/bootmanager.cpp

@@ -250,6 +250,7 @@ void GRenderWindow::mouseReleaseEvent(QMouseEvent* event) {
 }
 
 void GRenderWindow::TouchBeginEvent(const QTouchEvent* event) {
+    // TouchBegin always has exactly one touch point, so take the .first()
     const auto [x, y] = ScaleTouch(event->touchPoints().first().pos());
     this->TouchPressed(x, y);
 }

src/citra_qt/bootmanager.h

@@ -9,13 +9,13 @@
 #include <mutex>
 #include <QGLWidget>
 #include <QThread>
-#include <QTouchEvent>
 #include "common/thread.h"
 #include "core/core.h"
 #include "core/frontend/emu_window.h"
 
 class QKeyEvent;
 class QScreen;
+class QTouchEvent;
 
 class GGLWidgetInternal;
 class GMainWindow;