[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/dib.cpp

@@ -241,6 +241,7 @@ HBITMAP InitializeImage(LPCWSTR name, LPWIN32_FIND_DATAW pFound, BOOL isFile)
 HBITMAP SetBitmapAndInfo(HBITMAP hBitmap, LPCWSTR name, LPWIN32_FIND_DATAW pFound, BOOL isFile)
 {
     // update image
+    canvasWindow.resetScrollPos();
     imageModel.PushImageForUndo(hBitmap);
     imageModel.ClearHistory();