For wxMSW text controls with wxTE_RICH2 style, calling SetFont() counts
as an undoable operation, resulting in CanUndo() returning true even if
no "real" changes have been made yet.
Fix this by resetting the undo stack after creating the control using
ITextDocument::Undo().
Unfortunately this interface is not available in MinGW-32, so this fix
can't be used with it.
Closes https://github.com/wxWidgets/wxWidgets/pull/2010Closes#17524.