Destroy the in-place edit control in wxGenericListCtrl dtor.

Destroy the in-place edit control in wxGenericListCtrl dtor.

If the in-place text control was still alive when wxGenericListCtrl was
destroyed, it resulted in asserts from wxWindow dtor about child windows still
being alive, so explicitly destroy it from wxListMainWindow dtor.

As this required a slightly different behaviour from wxListTextCtrlWrapper::
EndEdit(), replace its bool argument with an enum one which can take more than
2 values. Not using bool values when calling it also made the code more clear.

Finally, added a unit test verifying that the in-place control is indeed
destroyed correctly.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65769 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775