Fix hit testing in generic wxDataViewToggleRenderer.

Handle clicks on the checkboxes in generic wxDataViewCtrl correctly by taking
into account that the checkbox rectangle is centred inside the total cell
rectangle.

Closes #15144.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73835 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775