Correct HasFocus() to work with subwindows of a composite control.

Correct HasFocus() to work with subwindows of a composite control.

When a subwindow (i.e. one that overrides GetMainWindowOfCompositeControl() to
return a parent window) has focus, HasFocus() should return true for it too,
in addition to returning true for the main window.

This completes the fix of r69788.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69860 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775