Partial solution for WinForms ComboBox.

For some reason, in UIA v3 ComboBox doesn't expose ExpandCollapsePattern. Instead it has button "Open" which can be clicked. This change abstracts required changes away.
On Application.Close() instead of closing main window only it is better to close everything we can - there can be more than one window, e.g. in case of multi-threaded UI case.
Removed focus setting all the time