Check wxListCtrl::GetItemRect() origin in the unit tests.

Check wxListCtrl::GetItemRect() origin in the unit tests.

Verify that the top item is _not_ at (0, 0) when the header is present in the
control, as the control client coordinates should not take the header into
account.

This test passes when using wxGenericListCtrl since r74197, add it to ensure
that it doesn't get broken again later.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74232 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775