Correct text position in wxDataViewCustomRenderer::RenderText() in wxGTK.

Correct text position in wxDataViewCustomRenderer::RenderText() in wxGTK.

It simply ignored the passed in rectangle meaning that the text was always
drawn at the top left corner of the cell rectangle.

Also more code cleanup: collect all render call parameters in a single struct
and provide a public function to set them all at once instead of making them
public.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62595 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775