Use correct cell alignment in generic wxDataViewCtrl mouse handling code.

Don't fall back to wxALIGN_CENTRE, even if the renderer doesn't specify its
own alignment we still have to take the column alignment in consideration, so
use GetEffectiveAlignment() (which had to be made public for this).

This notably fixes (again) hit testing for wxDataViewToggleRenderer in the
generic version.

Closes #15731.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75329 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775