Windows: ScrollContainer loses position when window is resized

[mhsmith]

To Reproduce

• Run the app from #1604 on Windows.
• Resize the window so the scroll bar is visible, and scroll down to the bottom.
• Resize the window again. Even the smallest change in the window size causes the scroll position to jump back to the top.

Expected behavior

When the window is resized, the scroll position should be retained as closely as possible.

Environment:

• Operating System: Windows 10
• Python version: 3.8
• Software versions:
  • Briefcase: 560c1aae87
  • Toga: 9a292f8

[mhsmith]

This is significantly improved by #1969. It now only happens when a widget inside the container is focused, in which case resizing the window will scroll the focused widget back into view.

This is a much less severe problem, so I think we can leave it for now.

[mhsmith]

Based on this discussion, this could be fixed with a one-line override of the ScrollToControl method. Unfortunately, Python.NET does not currently support overriding protected virtual methods (pythonnet/pythonnet#2192).