[MSPAINT] Reset scroll position in some situations (#5789)

In some situations, the scroll position should be reset.
- Add CCanvasWindow::resetScrollPos method.
- Reset the scroll position on loading a file.
- Reset the scroll position on mirroring/rotating
  the image.
CORE-19094

base/applications/mspaint/canvas.cpp

@@ -199,6 +199,12 @@ VOID CCanvasWindow::updateScrollInfo()
     SetScrollInfo(SB_VERT, &si);
 }
 
+VOID CCanvasWindow::resetScrollPos()
+{
+    SetScrollPos(SB_HORZ, 0);
+    SetScrollPos(SB_VERT, 0);
+}
+
 LRESULT CCanvasWindow::OnSize(UINT nMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
 {
     if (m_hWnd)